XYZ: Grant Negotiation Access Protocol
draft-richer-transactional-authz-09

Network Working Group                                     J. Richer, Ed.
Internet-Draft                                       Bespoke Engineering
Intended status: Standards Track                           July 25, 2020
Expires: January 26, 2021

                 XYZ: Grant Negotiation Access Protocol
                  draft-richer-transactional-authz-09

Abstract

   This document defines a mechanism for delegating authorization to a
   piece of software, and conveying that delegation to the software.

   This document is input into the GNAP working group and should be
   referred to as "XYZ" to differentiate it from other proposals.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 RFC 2119 [RFC2119] RFC 8174 [RFC8174] when, and only when, they
   appear in all capitals, as shown here.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 26, 2021.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

Richer                  Expires January 26, 2021                [Page 1]
Internet-Draft             transactional-authz                 July 2020

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Protocol  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.1.  Parties . . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.2.  Sequences . . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Requesting Access . . . . . . . . . . . . . . . . . . . . . .   5
     2.1.  Requesting Resources  . . . . . . . . . . . . . . . . . .   7
       2.1.1.  Requesting a Single Access Token  . . . . . . . . . .   7
       2.1.2.  Requesting Multiple Access Tokens . . . . . . . . . .   9
     2.2.  Requesting User Information . . . . . . . . . . . . . . .  10
     2.3.  Identifying the Client  . . . . . . . . . . . . . . . . .  11
     2.4.  Identifying the User  . . . . . . . . . . . . . . . . . .  12
     2.5.  Interacting with the User . . . . . . . . . . . . . . . .  14
       2.5.1.  Redirect to an Arbitrary URL  . . . . . . . . . . . .  14
       2.5.2.  Redirect to an Arbitrary Short URL  . . . . . . . . .  15
       2.5.3.  Open an Application-specific URL  . . . . . . . . . .  15
       2.5.4.  Receive a Browser-based Callback  . . . . . . . . . .  16
       2.5.5.  Receive an HTTP Direct Callback . . . . . . . . . . .  17
       2.5.6.  Display a Short Code  . . . . . . . . . . . . . . . .  18
       2.5.7.  Extending Interaction Capabilities  . . . . . . . . .  18
     2.6.  Providing Displayable Client Information  . . . . . . . .  18
     2.7.  Declaring Client Capabilities . . . . . . . . . . . . . .  19
     2.8.  Referencing an Existing Grant Request . . . . . . . . . .  19
     2.9.  Extending The Grant Request . . . . . . . . . . . . . . .  19
   3.  Grant Response  . . . . . . . . . . . . . . . . . . . . . . .  20
     3.1.  Request Continuation Handle . . . . . . . . . . . . . . .  20
     3.2.  Access Tokens . . . . . . . . . . . . . . . . . . . . . .  21
       3.2.1.  Single Access Token . . . . . . . . . . . . . . . . .  21
       3.2.2.  Multiple Access Tokens  . . . . . . . . . . . . . . .  22
     3.3.  Interaction Capabilities  . . . . . . . . . . . . . . . .  23
       3.3.1.  Redirection to an arbitrary URL . . . . . . . . . . .  24
       3.3.2.  Redirection to a short URL  . . . . . . . . . . . . .  24
       3.3.3.  Launch of an application URL  . . . . . . . . . . . .  25
       3.3.4.  Callback to a Client URL  . . . . . . . . . . . . . .  25
       3.3.5.  Push to a Client URL  . . . . . . . . . . . . . . . .  25
       3.3.6.  Display of a Short Code . . . . . . . . . . . . . . .  26
       3.3.7.  Extending Interaction Capability Responses  . . . . .  27
     3.4.  Returning User Information  . . . . . . . . . . . . . . .  27

Richer                  Expires January 26, 2021                [Page 2]
Internet-Draft             transactional-authz                 July 2020

     3.5.  Returning Dynamically-bound Reference Handles . . . . . .  27
     3.6.  Error response  . . . . . . . . . . . . . . . . . . . . .  28
     3.7.  Extending the Response  . . . . . . . . . . . . . . . . .  29
   4.  Interaction at the AS . . . . . . . . . . . . . . . . . . . .  29
     4.1.  Interaction at a Redirected URI . . . . . . . . . . . . .  30
     4.2.  Interaction at the User Code URI  . . . . . . . . . . . .  30
     4.3.  Interaction through an Application URI  . . . . . . . . .  30
     4.4.  Post-Interaction Completion . . . . . . . . . . . . . . .  31
       4.4.1.  Completing Interaction with a Callback URI  . . . . .  31
       4.4.2.  Completing Interaction with a Pushback URI  . . . . .  32
       4.4.3.  Calculating the interaction hash  . . . . . . . . . .  33
   5.  Continuing a Grant Request  . . . . . . . . . . . . . . . . .  34
     5.1.  Continuing after a Finalized Interaction  . . . . . . . .  35
     5.2.  Continuing after Tokens are Issued  . . . . . . . . . . .  35
   6.  Token Management  . . . . . . . . . . . . . . . . . . . . . .  35
     6.1.  Rotating the Access Token . . . . . . . . . . . . . . . .  35
     6.2.  Revoking the Access Token . . . . . . . . . . . . . . . .  36
   7.  Sending Access Tokens . . . . . . . . . . . . . . . . . . . .  37
   8.  Binding Keys  . . . . . . . . . . . . . . . . . . . . . . . .  37
     8.1.  Detached JWS  . . . . . . . . . . . . . . . . . . . . . .  38
     8.2.  Attached JWS  . . . . . . . . . . . . . . . . . . . . . .  40
     8.3.  Mutual TLS  . . . . . . . . . . . . . . . . . . . . . . .  41
     8.4.  DPoP  . . . . . . . . . . . . . . . . . . . . . . . . . .  42
     8.5.  HTTP Signing  . . . . . . . . . . . . . . . . . . . . . .  44
     8.6.  OAuth PoP . . . . . . . . . . . . . . . . . . . . . . . .  46
   9.  Discovery . . . . . . . . . . . . . . . . . . . . . . . . . .  47
   10. Resource Servers  . . . . . . . . . . . . . . . . . . . . . .  48
     10.1.  Introspecting a Token  . . . . . . . . . . . . . . . . .  48
     10.2.  Deriving a downstream token  . . . . . . . . . . . . . .  49
     10.3.  Registering a Resource Handle  . . . . . . . . . . . . .  50
     10.4.  Requesting a Resources Without a Token . . . . . . . . .  52
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  52
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  52
   13. Security Considerations . . . . . . . . . . . . . . . . . . .  52
   14. Privacy Considerations  . . . . . . . . . . . . . . . . . . .  53
   15. Normative References  . . . . . . . . . . . . . . . . . . . .  53
   Appendix A.  Document History . . . . . . . . . . . . . . . . . .  54
   Appendix B.  Component Data Models  . . . . . . . . . . . . . . .  56
   Appendix C.  Example Protocol Flows . . . . . . . . . . . . . . .  56
     C.1.  Redirect-Based User Interaction . . . . . . . . . . . . .  57
     C.2.  Secondary Device Interaction  . . . . . . . . . . . . . .  60
     C.3.  No User Involvement . . . . . . . . . . . . . . . . . . .  63
     C.4.  Asynchronous Authorization  . . . . . . . . . . . . . . .  64
     C.5.  Applying OAuth 2 Scopes and Client IDs  . . . . . . . . .  67
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  68

Richer                  Expires January 26, 2021                [Page 3]
Internet-Draft             transactional-authz                 July 2020

1.  Protocol

   This protocol allows a piece of software to request delegated
   authorization to an API, protected by an authorization server usually
   on behalf of a resource owner.  The user operating the software may
   interact with the authorization server to authenticate, provide
   consent, and authorize the request.

1.1.  Parties

   The Authorization Server (AS) manages the requested delegations.  It
   is defined by its grant endpoint, a single URL that accepts a POST
   request with a JSON payload.  The AS MAY also have other endpoints,
   including interaction endpoints and user code endpoints, and these
   are introduced to the RC as needed during the transaction process.

   The Resource Client (RC, aka "client") requests tokens from the AS
   and uses tokens at the RS.

   The Resource Server (RS) accepts tokens from the RC and validates
   them (potentially at the AS).

   The Resource Owner (RO) authorizes the request from the RC to the RS,
   often interactively at the AS.

   The Requesting Party (aka "user") operates the RC and may be the same
   party as the RO.

1.2.  Sequences

   The RC requests access to an RS, and the AS determines that it needs
   to interact with the user directly to get the RO's consent:

   1.  The RC creates a grant request and sends it to the AS (Section 2)

   2.  The AS processes the grant request and determines if the RO needs
       to interact and sends its response (Section 3)

   3.  If interaction is required, the AS interacts with the RO
       (Section 4), possibly by directing the RC to send the RO there

   4.  The RC continues the grant at the AS (Section 5)

   5.  The AS processes the transaction again, determining that a token
       can be issued

   6.  The AS issues a token to the RC

Richer                  Expires January 26, 2021                [Page 4]
Internet-Draft             transactional-authz                 July 2020

   7.  The RC uses the token with the RS

   [[ Editor's note: More sequences and common connections are needed.
   See Appendix C for more specific examples. ]]

2.  Requesting Access

   To start a request, the client sends JSON [RFC8259] document with an
   object as its root.  Each member of the request object represents a
   different aspect of the client's request.

   A non-normative example of a grant request is below:

Richer                  Expires January 26, 2021                [Page 5]
Internet-Draft             transactional-authz                 July 2020

   {
       "resources": [
           {
               "type": "photo-api",
               "actions": [
                   "read",
                   "write",
                   "dolphin"
               ],
               "locations": [
                   "https://server.example.net/",
                   "https://resource.local/other"
               ],
               "datatypes": [
                   "metadata",
                   "images"
               ]
           },
           "dolphin-metadata"
       ],
       "key": {
           "proof": "jwsd",
           "jwk": {
                       "kty": "RSA",
                       "e": "AQAB",
                       "kid": "xyz-1",
                       "alg": "RS256",
                       "n": "kOB5rR4Jv0GMeL...."
           }
       },
       "interact": {
           "redirect": true,
           "callback": {
               "uri": "https://client.example.net/return/123455",
               "nonce": "LKLTI25DK82FX4T4QFZC"
           }
       },
       "display": {
           "name": "My Client Display Name",
           "uri": "https://example.net/client"
       },
       "capabilities": ["ext1", "ext2"],
       "subject": {
           "sub_ids": ["iss-sub", "email"],
           "assertions": ["oidc_id_token"]
       }
   }

Richer                  Expires January 26, 2021                [Page 6]
Internet-Draft             transactional-authz                 July 2020

   The request MUST be sent as a JSON object in the body of the HTTP
   POST request with Content-Type "application/json", unless otherwise
   specified by the signature mechanism.

2.1.  Requesting Resources

   If the client is requesting one or more access tokens for the purpose
   of accessing an API, the client MUST include a resources element.
   This element MUST be an array (for a single access token) or an
   object (for multiple access tokens), as described in the following
   sections.

2.1.1.  Requesting a Single Access Token

   When requesting a single access token, the client MUST send a
   resources element containing a JSON array.  The elements of the JSON
   array represent rights of access that the client is requesting in the
   access token.  The requested access is the sum of all elements within
   the array.  These request elements MAY be sent by value as an object
   or by reference as a string.  A single resources array MAY contain
   both object and string type resource requests.

   The client declares what access it wants to associated with the
   resulting access token using objects that describe multiple
   dimensions of access.  Each object contains a "type" property that
   determines the type of API that the client is calling.  The value of
   this field is under the control of the AS and it MAY determine which
   other fields allowed in the object.  While it is expected that many
   APIs will have its own properties, a set of common properties are
   defined here.  Specific API implementations SHOULD NOT re-use these
   fields with different semantics or syntax.  [[ Editor's note: this
   will align with OAuth 2 RAR, but the details of how it aligns are TBD
   ]].

   actions  The types of actions the RC will take at the RS as an array
      of strings.  The values of the strings are determined by the API
      being protected.

   locations  The location of the RS as an array of strings.  These
      strings are typically URIs, and are determined by the API being
      protected.

   datatypes  Kinds of data available to the RC at the RS's API as an
      array of strings.  The values of the strings are determined by the
      API being protected.

Richer                  Expires January 26, 2021                [Page 7]
Internet-Draft             transactional-authz                 July 2020

   identifier  A string identifier indicating a specific resource at the
      RS.  The value of the string is determined by the API being
      protected.

   The following non-normative example shows the use of both common and
   API-specific elements.

       "resources": [
           {
               "type": "photo-api",
               "actions": [
                   "read",
                   "write",
                   "dolphin"
               ],
               "locations": [
                   "https://server.example.net/",
                   "https://resource.local/other"
               ],
               "datatypes": [
                   "metadata",
                   "images"
               ]
           },
           {
               "type": "financial-transaction",
               "actions": [
                   "withdraw"
               ],
               "identifier": "account-14-32-32-3",
               "currency": "USD"
           }
       ]

   Instead of sending an object, a client MAY send a string known to the
   AS or RS representing the access being requested.  Each string SHOULD
   correspond to a specific expanded object representation at the AS. [[
   Editor's note: we could describe more about how the expansion would
   work.  For example, expand into an object where the value of the
   "type" field is the value of the string.  Or we could leave it open
   and flexible, since it's really up to the AS/RS to interpret. ]] This
   value is opaque to the client and MAY be any valid JSON string, and
   therefore could include spaces, unicode characters, and properly
   escaped string sequences.

       "resources": [
           "read", "dolphin-metadata", "some other thing"
       ]

Richer                  Expires January 26, 2021                [Page 8]
Internet-Draft             transactional-authz                 July 2020

   A single "resources" array MAY include both object-type and string-
   type resource items.

       "resources": [
           {
               "type": "photo-api",
               "actions": [
                   "read",
                   "write",
                   "dolphin"
               ],
               "locations": [
                   "https://server.example.net/",
                   "https://resource.local/other"
               ],
               "datatypes": [
                   "metadata",
                   "images"
               ]
           },
           "read", "dolphin-metadata",
           {
               "type": "financial-transaction",
               "actions": [
                   "withdraw"
               ],
               "identifier": "account-14-32-32-3",
               "currency": "USD"
           },
           "some other thing"
       ]

2.1.2.  Requesting Multiple Access Tokens

   When requesting multiple access tokens, the resources element is a
   JSON object.  The names of the JSON object elements are token
   identifiers chosen by the client, and MAY be any valid string.  The
   values of the JSON object are JSON arrays representing a single
   access token request, as specified in requesting a single access
   token (Section 3.2.1).

   The following non-normative example shows a request for two separate
   access tokens, token1 and token2.

Richer                  Expires January 26, 2021                [Page 9]
Internet-Draft             transactional-authz                 July 2020

       "resources": {
           "token1": [
             {
                 "type": "photo-api",
                 "actions": [
                     "read",
                     "write",
                     "dolphin"
                 ],
                 "locations": [
                     "https://server.example.net/",
                     "https://resource.local/other"
                 ],
                 "datatypes": [
                     "metadata",
                     "images"
                 ]
             },
             "dolphin-metadata"
         ],
         "token2": [
               {
                   "type": "walrus-access",
                   "actions": [
                       "foo",
                       "bar"
                   ],
                   "locations": [
                       "https://resource.other/"
                   ],
                   "datatypes": [
                       "data",
                       "pictures",
                       "walrus whiskers"
                   ]
               }
           ]
       }

2.2.  Requesting User Information

   If the client is requesting information about the current user from
   the AS, it sends a subject element as a JSON object.  This object MAY
   contain the following fields (or additional fields defined in [[
   registry TBD ]]).

   sub_ids  An array of subject identifier subject types requested for
      the user, as defined by [I-D.ietf-secevent-subject-identifiers].

Richer                  Expires January 26, 2021               [Page 10]
Internet-Draft             transactional-authz                 July 2020

   assertions  An array of requested assertion formats defined by [[
      registry TBD ]].

   "subject": {
      "sub_ids": [ "iss-sub", "email" ],
      "assertions": [ "oidc-id-token", "saml" ]
   }

   If the AS knows the identifier for the current user and has
   permission to do so [[ editor's note: from the user's consent or a
   policy or ... ]], the AS MAY return the user's information in its
   response (Section 3.4).

   The "sub-ids" and "assertions" request fields are independent of each
   other, and a returned assertion MAY omit a requested subject
   identifier. [[ Editor's note: we're potentially conflating these two
   fields in the same structure, so perhaps these should be split. ]]

2.3.  Identifying the Client

   When sending an initial request to the AS, the client MUST identify
   itself by including the key field in the request and by signing the
   request as described in Section 8.  This key MAY be sent by value or
   by reference.

   When sent by value, the key MUST be a public key in at least one
   supported format and MUST contain a proof property that matches the
   proofing mechanism used in the request.  If the key is sent in
   multiple formats, all the keys MUST be the same.  The key presented
   in this field MUST be the key used to sign the request.

   proof  The form of proof that the RC will use when presenting the key
      to the AS.  The valid values of this field and the processing
      requirements for each are detailed in Section 8.  This field is
      REQUIRED.

   jwk  Value of the public key as a JSON Web Key. MUST contain an "alg"
      field which is used to validate the signature.  MUST contain the
      "kid" field to identify the key in the signed object.

   cert  PEM serialized value of the certificate used to sign the
      request, with optional internal whitespace.

   cert#256  The certificate thumbprint calculated as per OAuth-MTLS
      [RFC8705] in base64 URL encoding.

   Additional key types are defined in [[ registry TBD ]].  Proof types
   are defined in a [[ registry TBD ]] and described in Section 8. [[

Richer                  Expires January 26, 2021               [Page 11]
Internet-Draft             transactional-authz                 July 2020

   Editor's note: we will eventually want to have fetchable keys, I
   would guess.  Things like DID for key identification are going to be
   important. ]]

   This non-normative example shows a single key presented in multiple
   formats using a single proofing mechanism.

    "key": {
        "proof": "httpsig",
        "jwk": {
                    "kty": "RSA",
                    "e": "AQAB",
                    "kid": "xyz-1",
                    "alg": "RS256",
                    "n": "kOB5rR4Jv0GMeLaY6_It_r3ORwdf8ci_JtffXyaSx8xY..."
        },
        "cert": "MIIEHDCCAwSgAwIBAgIBATANBgkqhkiG9w0BAQsFA..."
    }

   The AS MAY associate policies with the client software identified by
   this key, such as limiting which resources can be requested and which
   interaction methods can be used.

   If the client has a reference for its key, the client MAY send that
   reference handle as a string.  The format of this string is opaque to
   the client.

   {
     "key": "7C7C4AZ9KHRS6X63AJAO"
   }

   If the key is passed by reference, the proofing mechanism associated
   with that key reference MUST also be used.  If the AS does not
   recognize the key reference handle, the request MUST be rejected with
   an error.

   If the client identifies its key by reference, the referenced key MAY
   be a symmetric key known to the AS.  The client MUST NOT send a
   symmetric key by value.

   The AS MUST ensure that the key represented by this reference is the
   same key used to sign the request as described in Section 8.

2.4.  Identifying the User

   If the client knows the identity of the current user or one or more
   identifiers for the user, the client MAY send that information to the

Richer                  Expires January 26, 2021               [Page 12]
Internet-Draft             transactional-authz                 July 2020

   AS in the "user" field.  The client MAY pass this information by
   value or by reference.

   sub_ids  An array of subject identifiers for the user, as defined by
      [I-D.ietf-secevent-subject-identifiers].

   assertions  An object containing assertions as values keyed on the
      assertion type defined by [[ registry TBD ]]. [[ Editor's note:
      should this be an array of objects with internal typing like the
      sub-ids?  Do we expect more than one assertion per user anyway? ]]

   "user": {
      "sub_ids": [ {
        "subject_type": "email",
        "email": "user@example.com"
      } ],
      "assertions": {
        "oidc_id_token": "eyj..."
      }
   }

   Subject identifiers are hints to the AS in determining the current
   user and MUST NOT be taken as declarative statements that a
   particular user is present at the client.  Assertions SHOULD be
   validated by the AS. [[ editor's note: assertion validation is
   extremely specific to the kind of assertion in place ]]

   If the identified user does not match the user present at the AS
   during an interaction step, the AS SHOULD reject the request. [[
   Editor's note: we're potentially conflating identification (sub-ids)
   and provable presence (assertions and a trusted reference handle) in
   the same structure, so perhaps these should be split. ]]

   Additional user assertion formats are defined in [[ registry TBD --
   probably the same registry as requesting formats ]].

   If the client has a reference for the current user at this AS, the
   client MAY pass that reference as a string.  The format of this
   string is opaque to the client.

   "user": "XUT2MFM1XBIKJKSDU8QM"

   If the AS trusts the client to present user information, it MAY
   decide, based on its policy, to skip interaction with the user, even
   if the client provides one or more interaction capabilities.

Richer                  Expires January 26, 2021               [Page 13]
Internet-Draft             transactional-authz                 July 2020

2.5.  Interacting with the User

   If the client is capable of driving interaction with the user, the
   client SHOULD declare the means that it can interact using the
   "interact" field.  This field is a JSON object with keys that declare
   different interaction capabilities.  A client MUST NOT declare an
   interaction capability it does not support.

   The client MAY send multiple capabilities in the same request.  There
   is no preference order specified in this request.  An AS MAY respond
   to any, all, or none of the presented interaction capabilities
   (Section 3.3) in a request, depending on its capabilities and what is
   allowed to fulfill the request.

   The following sections detail requests for interaction capabilities.
   Additional interaction capabilities are defined in [[ a registry TBD
   ]].

   [[ Editor's note: there need to be more examples (Appendix C) that
   knit together the interaction capabilities into common flows, like an
   authz-code equivalent.  But it's important for the protocol design
   that these are separate pieces to allow such knitting to take place.
   ]]

       "interact": {
           "redirect": true,
           "user_code": true,
           "callback": {
               "uri": "https://client.example.net/return/123455",
               "nonce": "LKLTI25DK82FX4T4QFZC"
           }
       }

2.5.1.  Redirect to an Arbitrary URL

   If the client is capable of directing the user to a URL defined by
   the AS at runtime, the client indicates this by sending the
   "redirect" field with the boolean value "true".  The means by which
   the client will activate this URL is out of scope of this
   specification, but common methods include an HTTP redirect, launching
   a browser on the user's device, providing a scannable image encoding,
   and printing out a URL to an interactive console.

   "interact": {
      "redirect": true
   }

Richer                  Expires January 26, 2021               [Page 14]
Internet-Draft             transactional-authz                 July 2020

   If this interaction capability is supported for this client and
   request, the AS returns a redirect interaction response
   Section 3.3.1.

2.5.2.  Redirect to an Arbitrary Short URL

   If the client can redirect to a shortened URL defined by the AS at
   runtime, the client indicates this by sending the "redirect" field
   with the boolean value "true".  The means by which the client will
   activate this URL is out of scope of this specification, but common
   methods include an HTTP redirect, launching a browser on the user's
   device, providing a scannable image encoding, and printing out a URL
   to an interactive console.

   "interact": {
      "redirect_short": true
   }

   If this interaction capability is supported for this client and
   request, the AS returns a redirect interaction response with short
   URL Section 3.3.2.

   [[ Editor's note: I'm not sold on this structure as there's a lot of
   overlap with the "redirect" capability, so maybe these should merge
   somehow.  Also, I'm not sure if we want additional parameters in
   here, like a max length that the client can support?  These could
   also be folded into a general "redirect" pattern. ]]

2.5.3.  Open an Application-specific URL

   If the client can open a URL associated with an application on the
   user's device, the client indicates this by sending the "app" field
   with boolean value "true".  The means by which the client determines
   the application to open with this URL are out of scope of this
   specification.

   "interact": {
      "app": true
   }

   If this interaction capability is supported for this client and
   request, the AS returns an app interaction response with an app URL
   payload Section 3.3.3.

   [[ Editor's note: this is also similar to the "redirect" above today
   as most apps use captured URLs, but there seems to be a desire for
   splitting the web-based interaction and app-based interaction into

Richer                  Expires January 26, 2021               [Page 15]
Internet-Draft             transactional-authz                 July 2020

   different URIs.  There's also the possibility of wanting more in the
   payload than can be reasonably put into the URL. ]]

2.5.4.  Receive a Browser-based Callback

   If the client is capable of receiving a callback through the user's
   browser at the completion of an interaction, the client indicates
   this by sending the "callback" field.  The value of this field is an
   object containing the following members.

   uri  REQUIRED.  Indicates the URI to send the RO to after
      interaction.  This URI MAY be unique per request and MUST be
      hosted by or accessible by the RC.  This URI MUST NOT contain any
      fragment component.  This URI MUST be protected by HTTPS, be
      hosted on a server local to the user's browser ("localhost"), or
      use an application-specific URI scheme.  If the RC needs any state
      information to tie to the front channel interaction response, it
      MUST encode that into the callback URI.  The allowable URIs and
      URI patterns MAY be restricted by the AS based on the RC's
      presented key information.  The callback URI SHOULD be presented
      to the RO during the interaction phase before redirect.

   nonce  REQUIRED.  Unique value to be used in the calculation of the
      "hash" query parameter on the callback URL, must be sufficiently
      random to be unguessable by an attacker.  MUST be generated by the
      RC as a unique value for this request.

   hash_method  OPTIONAL.  The hash calculation mechanism to be used for
      the callback hash in Section 4.4.3.  Can be one of sha3 or sha2.
      If absent, the default value is sha3. [[ Editor's note: This
      should be expandable via a registry of cryptographic options, and
      it would be good if we didn't define our own identifiers here.  ]]

   "interact": {
       "callback": {
          "uri": "https://client.example.net/return/123455",
          "nonce": "LKLTI25DK82FX4T4QFZC"
       }
   }

   If this interaction capability is supported for this client and
   request, the AS returns a nonce for use in validating the callback
   response (Section 3.3.4).  Requests to the callback URI MUST be
   processed as described in [[ processing interaction callbacks ]], and
   the AS MUST require presentation of an interaction callback reference
   as described in Section 4.4.1.

Richer                  Expires January 26, 2021               [Page 16]
Internet-Draft             transactional-authz                 July 2020

   Since the incoming request to the callback URL is from the user's
   browser, the client MUST require the user to be present on the
   connection.  If used with the "pushback" parameter, the two URLs
   SHOULD be different as they have different security properties.

   Note that the means by which the user arrives at the AS is declared
   separately from the user's return using this callback mechanism.

2.5.5.  Receive an HTTP Direct Callback

   If the client is capable of receiving an HTTP message directly from
   the AS, the client indicates this by sending the "pushback" field.
   The value of this field is an object containing the following
   members.

   uri  REQUIRED.  Indicates the URI to send a message to after the RO
      is finished interacting.  This URI MAY be unique per request and
      MUST be hosted by or accessible by the RC.  This URI MUST NOT
      contain any fragment component.  This URI MUST be protected by
      HTTPS and MUST be reachable by the AS.  The allowable URIs and URI
      patterns MAY be restricted by the AS based on the RC's presented
      key information.

   nonce  REQUIRED.  Unique value to be used in the calculation of the
      "hash" value sent to the pushback URL, must be sufficiently random
      to be unguessable by an attacker.  MUST be generated by the RC as
      a unique value for this request.

   hash_method  OPTIONAL.  The signature mechanism to be used for the
      callback hash in Section 4.4.3.  Can be one of sha3 or sha2.  If
      absent, the default value is sha3. [[ Editor's note: This should
      be expandable via a registry of cryptographic options, and it
      would be good if we didn't define our own identifiers here.  ]]

   "interact": {
       "pushback": {
          "uri": "https://client.example.net/push/554321",
          "nonce": "82FX4T4QFZCLKLTI25DK"
       }
   }

   If this interaction capability is supported for this client and
   request, the AS returns a nonce for use in validating the pushback
   response (Section 3.3.5).  Requests to the pushback URI MUST be
   processed as described in Section 4.4.2, and the AS MUST require
   presentation of an interaction callback reference as described in [
   interaction callback references ].

Richer                  Expires January 26, 2021               [Page 17]
Internet-Draft             transactional-authz                 July 2020

   Since the incoming request to the pushback URL is from the AS and not
   from the user's browser, the client MUST NOT require the user to be
   present.  If used with the "callback" parameter, the two URLs SHOULD
   be different as they have different security properties.

   Note that the means by which the user arrives at the AS is declared
   separately from the user's return using this mechanism.

2.5.6.  Display a Short Code

   If the client is capable of displaying or otherwise communicating a
   short, human-entered code to the user, the client indicates this by
   sending the "user_code" field with the boolean value "true".  This
   code is to be entered at a static URL that does not change at
   runtime.

   "interact": {
       "user_code": true
   }

   If this interaction capability is supported for this client and
   request, the AS returns a user code and interaction URL as specified
   in Section 4.2.

2.5.7.  Extending Interaction Capabilities

   Additional interaction capabilities are defined in [[ a registry TBD
   ]].

   [[ Editor's note: we should have guidance in here about how to define
   other interaction capabilities.  There's already interest in defining
   message-based protocols and challenge-response protocols, for
   example. ]]

2.6.  Providing Displayable Client Information

   If the client has additional information to display to the user
   during any interactions at the AS, it MAY send that information in
   the "display" field.  This field is a JSON object that declares
   information to present to the user during any interactive sequences.

   name  Display name of the RC software

   uri  User-facing web page of the RC software

   logo_uri  Display image to represent the RC software

Richer                  Expires January 26, 2021               [Page 18]
Internet-Draft             transactional-authz                 July 2020

       "display": {
           "name": "My Client Display Name",
           "uri": "https://example.net/client"
       }

   Additional display fields are defined by [[ a registry TBD. ]]

   The AS SHOULD use these values during interaction with the user.  The
   AS MAY restrict display values to specific clients, as identified by
   their keys.

   [[ Editor's note: this might make sense to combine with the "key"
   field, but some classes of more dynamic client vary those fields
   separately.  We should also consider things like signed statements
   for client attestation, but that might fit better into a different
   top-level field instead. ]]

2.7.  Declaring Client Capabilities

   If the client supports extension capabilities, it MAY present them to
   the AS in the "capabilities" field.  This field is an array of
   strings representing specific extensions and capabilities, as defined
   by [[ a registry TBD ]].

   "capabilities": ["ext1", "ext2"]

2.8.  Referencing an Existing Grant Request

   If the client has a reference handle from a previously granted
   request, it MAY send that reference in the "reference" field.  This
   field is a single string.

   "existing_grant": "80UPRY5NM33OMUKMKSKU"

   The AS MUST dereference the grant associated with the reference and
   process this request in the context of the referenced one.

   [[ Editor's note: this basic capability is to allow for both step-up
   authorization and downscoped authorization, but by explicitly
   creating a new request and not modifying an existing one.  What's the
   best guidance for how an AS should process this? ]]

2.9.  Extending The Grant Request

   The request object MAY be extended by registering new items in [[ a
   registry TBD ]].  Extensions SHOULD be orthogonal to other
   parameters.  Extensions MUST document any aspects where the

Richer                  Expires January 26, 2021               [Page 19]
Internet-Draft             transactional-authz                 July 2020

   [[ Editor's note: we should have more guidance and examples on what
   possible top-level extensions would look like.  Things like an OIDC
   "claims" request or a VC query, for example. ]]

3.  Grant Response

   In response to a client's request, the AS responds with a JSON object
   as the HTTP entity body.

{
    "access_token": {
        "value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
        "proof": "bearer",
        "manage": "https://server.example.com/token/PRY5NM33OM4TB8N6BW7OZB8CDFONP219RP1L"
    },
    "continue": {
        "handle": "80UPRY5NM33OMUKMKSKU",
        "uri": "https://server.example.com/continue"
    },
    "subject": {
        "sub_ids": [ {
           "subject_type": "email",
           "email": "user@example.com",
        } ]
    }
}

3.1.  Request Continuation Handle

   If the AS determines that the request can be continued with
   additional requests, it responds with the "continue" field.  This
   field contains a JSON object with the following properties.

   handle  REQUIRED.  A unique reference for the grant request.

   uri  REQUIRED.  The URI at which the client can make continuation
      requests.  This URI MAY vary per client or ongoing request, or MAY
      be stable at the AS.

   wait  RECOMMENDED.  The amount of time in integer seconds the client
      SHOULD wait after receiving this continuation handle and calling
      the URI.

   expires_in  OPTIONAL.  The number of seconds in which the handle will
      expire.  The client MUST NOT use the handle past this time.  The
      handle MAY be revoked at any point prior to its expiration.

Richer                  Expires January 26, 2021               [Page 20]
Internet-Draft             transactional-authz                 July 2020

   {
       "continue": {
           "handle": "80UPRY5NM33OMUKMKSKU",
           "uri": "https://server.example.com/continue",
           "wait": 60
       }
   }

   The client can use the values of this field as described in
   Section 5.

   This field SHOULD be returned when interaction is expected, to allow
   the client to follow up after interaction has been concluded.

3.2.  Access Tokens

   If the AS has successfully granted one or more access tokens, it
   responds with one of these fields.  The AS MUST NOT respond with both
   fields.

   [[ Editor's note: I really don't like the dichotomy between
   "access_token" and "multiple_access_tokens" and their being mutually
   exclusive, and I think we should design away from this pattern toward
   something less error-prone. ]]

3.2.1.  Single Access Token

   If the client has requested a single access token and the AS has
   granted that access token, the AS responds with the "access_token"
   field.  The value of this field is an object with the following
   properties.

   value  REQUIRED.  The value of the access token as a string.  The
      value is opaque to the client.  The value SHOULD be limited to
      ASCII characters to facilitate transmission over HTTP headers and
      elements without additional encoding.

   proof  REQUIRED.  The proofing presentation mechanism used for
      presenting this access token to an RS.  See the section on sending
      access tokens (Section 7) for details on possible values to this
      field and their requirements.

   manage  OPTIONAL.  The management URI for this access token.  If
      provided, the client MAY manage its access token as described in
      managing an access token lifecycle (Section 6).  This URI MUST NOT
      include the access token value and MAY be different for each
      access token.

Richer                  Expires January 26, 2021               [Page 21]
Internet-Draft             transactional-authz                 July 2020

   resources  OPTIONAL.  A description of the rights associated with
      this access token, as defined in requesting resource access
      (Section 3.2.1).  If included, this MUST reflect the rights
      associated with the issued access token.  These rights MAY vary
      from what was requested by the client.

   expires_in  OPTIONAL.  The number of seconds in which the access will
      expire.  The client MUST NOT use the access token past this time.
      The access token MAY be revoked at any point prior to its
      expiration.

   key  The key that the token is bound to, REQUIRED if the token is
      sender-constrained.  The key MUST be in a format described in
      Section 2.3. [[ Editor's note: this isn't quite right, since the
      request section includes a "proof" field that we already have
      here.  A possible solution would be to only have a "key" field as
      defined above and its absence indicates a bearer token? ]]

    "access_token": {
        "value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
        "proof": "bearer",
        "manage": "https://server.example.com/token/PRY5NM33OM4TB8N6BW7OZB8CDFONP219RP1L",
        "resources": [
            {
                "type": "photo-api",
                "actions": [
                    "read",
                    "write",
                    "dolphin"
                ],
                "locations": [
                    "https://server.example.net/",
                    "https://resource.local/other"
                ],
                "datatypes": [
                    "metadata",
                    "images"
                ]
            },
            "read", "dolphin-metadata"
        ]
    }

3.2.2.  Multiple Access Tokens

   If the client has requested multiple access tokens and the AS has
   granted at least one of them, the AS responds with the
   "multiple_access_tokens" field.  The value of this field is a JSON

Richer                  Expires January 26, 2021               [Page 22]
Internet-Draft             transactional-authz                 July 2020

   object, and the property names correspond to the token identifiers
   chosen by the client in the multiple access token request
   (Section 2.1.2).  The values of the properties of this object are
   access tokens as described in Section 3.2.1.

    "multiple_access_tokens": {
        "token1": {
            "value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
            "proof": "bearer",
            "manage": "https://server.example.com/token/PRY5NM33OM4TB8N6BW7OZB8CDFONP219RP1L"
        },
        "token2": {
            "value": "UFGLO2FDAFG7VGZZPJ3IZEMN21EVU71FHCARP4J1",
            "proof": "bearer"
        }
    }

   Each access token corresponds to the named resources arrays in the
   client's request.  The AS MAY not issue one or more of the requested
   access tokens.  In such cases all of the issued access tokens are
   included without the omitted token.  The multiple access token
   response MUST be used when multiple access tokens are requested, even
   if only one access token is issued.

   If the client requested a single access token (Section 2.1.1), the AS
   MUST NOT respond with multiple access tokens.

   Each access token MAY have different proofing mechanisms.  If used,
   each access token MUST have different management URIs.

3.3.  Interaction Capabilities

   If the client has indicated a capability to interact with the user in
   its request (Section 2.5), and the AS has determined that interaction
   is both supported and necessary, the AS responds to the client with
   any of the following values.  There is no preference order for
   interaction capabilities in the response, and it is up to the client
   to determine which ones to use.

   The AS MUST NOT respond with any interaction capability that the
   client did not indicate in its request.

   [[ Editor's note: Currently these are all in the root of the
   response, but should they be bundled into an "interact" sub-object?
   This would match the request pattern. ]]

Richer                  Expires January 26, 2021               [Page 23]
Internet-Draft             transactional-authz                 July 2020

3.3.1.  Redirection to an arbitrary URL

   If the client indicates that it can redirect to an arbitrary URL
   (Section 2.5.1) and the AS supports this capability for the client's
   request, the AS responds with the "interaction_url" field, which is a
   string containing the URL to direct the user to.  This URL MUST be
   unique for the request and MUST NOT contain any security-sensitive
   information.

"interaction_url": "https://server.example.com/interact/4CF492MLVMSW9MKMXKHQ"

   The client sends the user to the URL to interact with the AS.  The
   client MUST NOT alter the URL in any way.  The means for the client
   to send the user to this URL is out of scope of this specification,
   but common methods include an HTTP redirect, launching the system
   browser, displaying a scannable code, or printing out the URL in an
   interactive console.

   [[ Editor's note: should we rename this to "redirect" to match the
   request?  Downside: it conflicts with OAuth 2's "redirect_uri"
   concept. ]]

3.3.2.  Redirection to a short URL

   If the client indicates that it can redirect to an arbitrary short
   URL (Section 2.5.2) and the AS supports this capability for the
   client's request, the AS responds with the "short_interaction_url"
   field, which is a string containing the URL to direct the user to.
   This URL MUST be unique for the request and MUST NOT contain any
   security-sensitive information.

   "short_interaction_url": "https://srv.ex/MXKHQ"

   The client sends the user to the URL to interact with the AS.  The
   client MUST NOT alter the URL in any way.  The means for the client
   to send the user to this URL is out of scope of this specification,
   but common methods include displaying a scannable code, or printing
   out the URL in an interactive console.

   [[ Editor's note: should we rename this to "short_redirect" to match
   the request?  Downside: it kinda conflicts with OAuth 2's
   "redirect_uri" concept.  This also could be folded into an object for
   interaction URIs with multiple options instead. ]]

Richer                  Expires January 26, 2021               [Page 24]
Internet-Draft             transactional-authz                 July 2020

3.3.3.  Launch of an application URL

   If the client indicates that it can launch an application URL
   (Section 2.5.3) and the AS supports this capability for the client's
   request, the AS responds with the "app" field, which is a string
   containing the URL to direct the user to.  This URL MUST be unique
   for the request and MUST NOT contain any security-sensitive
   information.

   "app_url": "https://app.example.com/launch?tx=4CF492MLV"

   The client launches the URL as appropriate on its platform, and the
   means for the client to launch this URL is out of scope of this
   specification.  The client MUST NOT alter the URL in any way.  The
   client MAY attempt to detect if an installed application will service
   the URL being sent.

   [[ Editor's note: This will probably need to be expanded to an object
   to account for other parameters needed in app2app use cases, like
   addresses for distributed storage systems, server keys, and the like.
   Details TBD as people build this out. ]]

3.3.4.  Callback to a Client URL

   If the client indicates that it can receive a post-interaction
   callback on a URL (Section 2.5.4) and the AS supports this capability
   for the client's request, the AS responds with a
   "callback_server_nonce" that the client will use in validating the
   callback as defined in Section 4.4.3.

   "callback_server_nonce": "MBDOFXG4Y5CVJCX821LH"

   If the AS returns a "callback_server_nonce", the client MUST NOT
   continue a grant request before it receives the associated
   interaction reference on the callback URI.  If both the "callback"
   and "pushback" capabilities are available, the client MAY use either
   value.

   [[ Editor's note: should we rename this "callback" and/or put it in
   an object to match the request?  That feels like an overfit to me,
   though. ]]

3.3.5.  Push to a Client URL

   If the client indicates that it can receive a post-interaction push
   on a URL (Section 2.5.5) and the AS supports this capability for the
   client's request, the AS responds with a "pushback_server_nonce" that

Richer                  Expires January 26, 2021               [Page 25]
Internet-Draft             transactional-authz                 July 2020

   the client will use in validating the pushback call as defined in
   Section 4.4.3.

   "pushback_server_nonce": "MBDOFXG4Y5CVJCX821LH"

   If the AS returns a "pushback_server_nonce", the client MUST NOT
   continue a grant request before it receives the associated
   interaction reference on the pushback URI.  If both the "callback"
   and "pushback" capabilities are available, the client MAY use either
   value.

   [[ Editor's note: should we rename this "pushback" and/or put it in
   an object to match the request?  That feels like an overfit to me,
   though. ]]

3.3.6.  Display of a Short Code

   If the client indicates that it can display a short user-typable code
   (Section 2.5.6) and the AS supports this capability for the client's
   request, the AS responds with a "user_code" field.  This field is an
   object that contains the following members.

   code  REQUIRED.  A unique short code that the user can type into an
      authorization server.  This string MUST be case-insensitive, MUST
      consist of only easily typeable characters (such as letters or
      numbers).  The time in which this code will be accepted SHOULD be
      short lived, such as several minutes.  It is RECOMMENDED that this
      code be no more than eight characters in length.

   url  RECOMMENDED.  The interaction URL that the RC will direct the RO
      to.  This URL MUST be stable at the AS such that clients can be
      statically configured with it.

       "user_code": {
           "code": "A1BC-3DFF",
           "url": "https://srv.ex/device"
       }

   The client MUST communicate the "code" to the user in some fashion,
   such as displaying it on a screen or reading it out audibly.  The
   client SHOULD also communicate the URL if possible.  As this
   interaction capability is designed to facilitate interaction via a
   secondary device, it is not expected that the client redirect the
   user to the URL.  If the client is capable of communicating an
   arbitrary URL to the user, such as through a scannable code, the
   client SHOULD use the "redirect" (Section 2.5.1) or "short_redirect"
   (Section 2.5.2) capabilities for this purpose.

Richer                  Expires January 26, 2021               [Page 26]
Internet-Draft             transactional-authz                 July 2020

3.3.7.  Extending Interaction Capability Responses

   Extensions to this specification can define new interaction
   capability responses in [[ a registry TBD ]].

3.4.  Returning User Information

   If information about the current user is requested and the AS grants
   the client access to that data, the AS returns the approved
   information in the "subject" response field.  This field is an object
   with the following OPTIONAL properties.

   sub_ids  An array of subject identifiers for the user, as defined by
      [I-D.ietf-secevent-subject-identifiers]. [[ Editor's note: privacy
      considerations are needed around returning identifiers. ]]

   assertions  An object containing assertions as values keyed on the
      assertion type defined by [[ registry TBD ]]. [[ Editor's note:
      should this be an array of objects with internal typing like the
      sub-ids?  Do we expect more than one assertion per user anyway? ]]

   updated_at  Timestamp in integer seconds indicating when the
      identified account was last updated.  The client MAY use this
      value to determine if it needs to request updated profile
      information through an identity API.

   "subject": {
      "sub_ids": [ {
        "subject_type": "email",
        "email": "user@example.com",
      } ],
      "assertions": {
        "oidc_id_token": "eyj..."
      }
   }

   Extensions to this specification MAY define additional response
   properties in [[ a registry TBD ]].

3.5.  Returning Dynamically-bound Reference Handles

   Many parts of the client's request can be passed as either a value or
   a reference.  Some of these references, such as for the client's keys
   or the resources, can sometimes be managed statically through an
   admin console or developer portal provided by the AS or RS.  If
   desired, the AS MAY also generate and return some of these references
   dynamically to the client in its response to facilitate multiple
   interactions with the same software.  The client SHOULD use these

Richer                  Expires January 26, 2021               [Page 27]
Internet-Draft             transactional-authz                 July 2020

   references in future requests in lieu of sending the associated data
   value.  These handles are intended to be used on future requests.

   Dynamically generated handles are string values that MUST be
   protected by the client as secrets.  Handle values MUST be
   unguessable and MUST NOT contain any sensitive information.  Handle
   values are opaque to the client. [[ Editor's note: these used to be
   objects to allow for expansion to future elements, like a management
   URI or different presentation types or expiration, but those weren't
   used in practice.  Is that desirable anymore or is collapsing them
   like this the right direction? ]]

   All dynamically generated handles are returned as fields in the root
   JSON object of the response.  This specification defines the
   following dynamic handle returns, additional handles can be defined
   [[ in a registry TBD ]].

   key_handle  A value used to represent the information in the key
      object that the client can use in a future request, as described
      in Section 2.3.

   display_handle  A value used to represent the information in the
      display object that the client can use in a future request, as
      described in Section 2.6.

   user_handle  A value used to represent the current user.  The client
      can use in a future request, as described in Section 2.4.

   This non-normative example shows two handles along side an issued
   access token.

   {
       "user_handle": "XUT2MFM1XBIKJKSDU8QM",
       "key_handle": "7C7C4AZ9KHRS6X63AJAO",
       "access_token": {
           "value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
           "proof": "bearer"
       }
   }

3.6.  Error response

   If the AS determines that the request cannot be issued for any
   reason, it responds to the RC with an error message.

   error  The error code.

Richer                  Expires January 26, 2021               [Page 28]
Internet-Draft             transactional-authz                 July 2020

   {

     "error": "user_denied"

   }

   The error code is one of the following, with additional values
   available in [[ a registry TBD ]]:

   user_denied  The RO denied the request.

   too_fast  The RC did not respect the timeout in the wait response.

   unknown_handle  The request referenced an unknown handle.

   [[ Editor's note: I think we will need a more robust error mechanism,
   and we need to be more clear about what error states are allowed in
   what circumstances.  Additionally, is the "error" parameter exclusive
   with others in the return? ]]

3.7.  Extending the Response

   Extensions to this specification MAY define additional fields for the
   grant response in [[ a registry TBD ]].

   [[ Editor's note: what guidance should we give to designers on this?
   ]]

4.  Interaction at the AS

   If the client indicates that it is capable of driving interaction
   with the user in its request (Section 2.5), and the AS determines
   that interaction is required and responds to one or more of the
   client's interaction capabilities, the client SHOULD initiate one of
   the returned interaction capabilities in the response (Section 3.3).

   When the RO is interacting with the AS, the AS MAY perform whatever
   actions it sees fit, including but not limited to:

   o  authenticate the user as RO

   o  gather consent and authorization from the RO for access to
      requested resources or the

   o  allow the RO to modify the parameters of the request (such as
      disallowing some requested resources or specifying an account or
      record)

Richer                  Expires January 26, 2021               [Page 29]
Internet-Draft             transactional-authz                 July 2020

   [[ Editor's note: there are some privacy and security considerations
   here but for the most part we don't want to be overly prescriptive
   about the UX, I think. ]]

4.1.  Interaction at a Redirected URI

   When the user is directed to the AS through the "interaction_url"
   (Section 3.3.1) or "short_interaction_url" (Section 3.3.2)
   capabilities, the AS can interact with the user through their web
   browser to authenticate the user as an RO and gather their consent.
   Note that since the client does not add any parameters to the URL,
   the AS MUST determine the grant request being referenced from the URL
   value itself.  If the URL cannot be associated with a currently
   active request, the AS MUST display an error to the user and MUST NOT
   attempt to redirect the user back to any client.

   The interaction URL MUST be reachable from the RO's browser, though
   note that the RO MAY open the URL on a separate device from the RC
   itself.  The interaction URL MUST be accessible from an HTTP GET
   request, and MUST be protected by HTTPS or equivalent means.

4.2.  Interaction at the User Code URI

   When the user is directed to the AS through the "user_code"
   (Section 3.3.6) capability, the AS can interact with the user through
   their web browser to collect the user code, authenticate the user as
   an RO, and gather their consent.  Note that since the URL itself is
   static, the AS MUST determine the grant request being referenced from
   the user code value itself.  If the user code cannot be associated
   with a currently active request, the AS MUST display an error to the
   user and MUST NOT attempt to redirect the user back to any client.

   The user code URL MUST be reachable from the RO's browser, though
   note that the RO MAY open the URL on a separate device from the RC
   itself.  The user code URL MUST be accessible from an HTTP GET
   request, and MUST be protected by HTTPS or equivalent means.

4.3.  Interaction through an Application URI

   When the user successfully launches an application through the "app"
   capability (Section 3.3.3), the AS interacts with the user through
   that application to authenticate the user as the RO and gather their
   consent.  The details of this interaction are out of scope for this
   specification.

   [[ Editor's note: Should we have anything to say about an app sending
   information to a back-end to get details on the pending request? ]]

Richer                  Expires January 26, 2021               [Page 30]
Internet-Draft             transactional-authz                 July 2020

4.4.  Post-Interaction Completion

   Upon completing an interaction with the user, if either a "callback"
   (Section 3.3.4) or "pushback" (Section 3.3.5) capability is available
   with the current request, the AS MUST follow the appropriate method
   at the end of interaction to allow the client to continue.  If
   neither capability is available, the AS SHOULD instruct the user to
   return to their client software upon completion.  Note that these
   steps still take place in most error cases, such as when the user has
   denied access.  This allows the client to potentially recover from
   the error state without restarting.

   [[ Editor's note: there might be some other kind of push-based
   notification or callback that the client can use, or an out-of-band
   non-HTTP protocol.  The AS would know about this if supported and
   used, but the guidance here should be written in such a way as to not
   be too restrictive in the next steps that it can take.  Still, it's
   important that the AS not expect or even allow clients to poll if the
   client has stated it can take a callback of some form, otherwise that
   sets up a potential session fixation attack vector that the client is
   trying to and able to avoid. ]]

   The AS MUST calculate a hash value as described in Section 4.4.3.
   The client will use this value to validate the return call from the
   AS.

   The AS MUST create an interaction reference and associate that
   reference with the current interaction and the underlying pending
   request.  This value MUST be sufficiently random so as not to be
   guessable by an attacker.

   The AS then MUST send the hash and interaction reference based on the
   interaction finalization capability as described in the following
   sections.  If both the "callback" and "pushback" capabilities are
   available for the current request, the AS MUST choose only one. [[
   Editor's note: is this restriction necessary? ]]

4.4.1.  Completing Interaction with a Callback URI

   When using the "callback" interaction capability (Section 3.3.4), the
   AS signals to the client that interaction is complete and the request
   can be continued by directing the user (in their browser) back to the
   client's callback URL sent in the callback request (Section 2.5.4).

   The AS secures this callback by adding the hash and interaction
   reference as query parameters to the client's callback URL.

Richer                  Expires January 26, 2021               [Page 31]
Internet-Draft             transactional-authz                 July 2020

   hash  REQUIRED.  The interaction hash value as described in
      Section 4.4.3.

   interact_ref  REQUIRED.  The interaction reference generated for this
      interaction.

   The means of directing the user to this URL are outside the scope of
   this specification, but common options include redirecting the user
   from a web page and launching the system browser with the target URL.

https://client.example.net/return/123455
  ?hash=p28jsq0Y2KK3WS__a42tavNC64ldGTBroywsWxT4md_jZQ1R2HZT8BOWYHcLmObM7XHPAdJzTZMtKBsaraJ64A
  &interact_ref=4IFWWIKYBC2PQ6U56NL1

   When receiving the request, the client MUST parse the query
   parameters to calculate and validate the hash value as described in
   Section 4.4.3.  If the hash validates, the client sends a
   continuation request to the AS as described in Section 5.1 using the
   interaction reference value received here.

4.4.2.  Completing Interaction with a Pushback URI

   When using the "pushback" interaction capability (Section 3.3.5), the
   AS signals to the client that interaction is complete and the request
   can be continued by sending an HTTP POST request to the client's
   pushback URL sent in the pushback request (Section 2.5.5).

   The entity message body is a JSON object consisting of the following
   two elements:

   hash  REQUIRED.  The interaction hash value as described in
      Section 4.4.3.

   interact_ref  REQUIRED.  The interaction reference generated for this
      interaction.

POST /push/554321 HTTP/1.1
Host: client.example.net
Content-Type: application/json

{
  "hash": "p28jsq0Y2KK3WS__a42tavNC64ldGTBroywsWxT4md_jZQ1R2HZT8BOWYHcLmObM7XHPAdJzTZMtKBsaraJ64A",
  "interact_ref": "4IFWWIKYBC2PQ6U56NL1"
}

   When receiving the request, the client MUST parse the JSON object and
   validate the hash value as described in Section 4.4.3.  If the hash
   validates, the client sends a continuation request to the AS as

Richer                  Expires January 26, 2021               [Page 32]
Internet-Draft             transactional-authz                 July 2020

   described in Section 5.1 using the interaction reference value
   received here.

4.4.3.  Calculating the interaction hash

   The "hash" parameter in the callback and pushback response ties the
   front channel response to an ongoing request by using values known
   only to the parties involved.  This prevents several kinds of session
   fixation attacks against the client.

   To calculate the "hash" value, the party doing the calculation first
   takes the "nonce" value sent by the RC in the interaction section of
   the initial request (Section 2.5.4), the AS's nonce value, and the
   "interact_ref" returned in the callback response.  For a "callback"
   return, the AS nonce is the "callback_server_nonce" value in the
   callback response (Section 3.3.4), while for a "pushback" return the
   AS nonce is the "pushback_server_nonce" value in the pushback
   response (Section 3.3.5).  These three values are concatenated to
   each other in this order using a single newline character as a
   separator between the fields.  There is no padding or whitespace
   before or after any of the lines, and no trailing newline character.

   VJLO6A4CAYLBXHTR0KRO
   MBDOFXG4Y5CVJCX821LH
   4IFWWIKYBC2PQ6U56NL1

   The party then hashes this string with the appropriate algorithm
   based on the "hash_method" parameter of the "callback" or "pushback"
   request.  If the "hash_method" value is not present in the RC's
   request, the algorithm defaults to "sha3". [[ Editor's note: these
   hash algorithms should be pluggable, and ideally we shouldn't
   redefine yet another crypto registry for this purpose, but I'm not
   convinced an appropriate one already exists. ]]

4.4.3.1.  SHA3

   The "sha3" hash method consists of hashing the input string with the
   512-bit SHA3 algorithm.  The byte array is then encoded using URL
   Safe Base64 with no padding.  The resulting string is the hash value.

p28jsq0Y2KK3WS__a42tavNC64ldGTBroywsWxT4md_jZQ1R2HZT8BOWYHcLmObM7XHPAdJzTZMtKBsaraJ64A

4.4.3.2.  SHA2

   The "sha2" hash method consists of hashing the input string with the
   512-bit SHA2 algorithm.  The byte array is then encoded using URL
   Safe Base64 with no padding.  The resulting string is the hash value.

Richer                  Expires January 26, 2021               [Page 33]
Internet-Draft             transactional-authz                 July 2020

62SbcD3Xs7L40rjgALA-ymQujoh2LB2hPJyX9vlcr1H6ecChZ8BNKkG_HrOKP_Bpj84rh4mC9aE9x7HPBFcIHw

5.  Continuing a Grant Request

   If the client receives a continuation element in its response
   Section 3.1, the client can make an HTTP POST call to the
   continuation URI with a JSON object.  The client MUST send the handle
   reference from the continuation element in its request as a top-level
   JSON parameter.

   {
     "handle": "tghji76ytghj9876tghjko987yh"
   }

   The client MAY include other parameters as described here or as
   defined [[ in a registry TBD ]]. [[ Editor's note: We probably want
   to allow other parameters, like modifying the resources requested or
   providing more user information.  We'll certainly have some kinds of
   specific challenge-response protocols as there's already been
   interest in that kind of thing, and the continuation request is the
   place where that would fit. ]]

   If a "wait" parameter was included in the continuation response, the
   client MUST NOT call the continuation URI prior to waiting the number
   of seconds indicated.  If no "wait" period is indicated, the client
   SHOULD wait at least 5 seconds [[ Editor's note: what's a reasonable
   amount of time so as not to DOS the server?? ]].

   The response from the AS is a JSON object and MAY contain any of the
   elements described in Section 3, with some variations:

   If the AS determines that the client can make a further continuation
   request, the AS MUST include a new "continue" response element
   (Section 3.1).  The returned handle value MUST NOT be the same as
   that used to make the continuation request, and the continuation URI
   MAY remain the same.  If the AS does not return a new "continue"
   response element, the client MUST NOT make an additional continuation
   request.  If a client does so, the AS MUST return an error.

   If the AS determines that the client still needs to drive interaction
   with the user, the AS MAY return appropriate responses for any of the
   interaction mechanisms (Section 3.3) the client indicated in its
   initial request (Section 2.5).  Unique values such as interaction
   URIs and nonces SHOULD be re-generated and not re-used.

   The client MUST present proof of the same key identified in the
   initial request (Section 2.3) by signing the request as described in
   Section 8.

Richer                  Expires January 26, 2021               [Page 34]
Internet-Draft             transactional-authz                 July 2020

5.1.  Continuing after a Finalized Interaction

   If the client has received an interaction reference from a "callback"
   (Section 4.4.1) or "pushback" (Section 4.4.2) incoming message, the
   client MUST include the "interaction_ref" in its continuation
   request.  Note that the client validates the hash before making the
   continuation request, but the client does not send the hash back to
   the AS.

   {
     "handle": "tghji76ytghj9876tghjko987yh",
     "interact_ref": "4IFWWIKYBC2PQ6U56NL1"
   }

5.2.  Continuing after Tokens are Issued

   A request MAY be continued even after access tokens have been issued,
   so long as the handle is valid.

6.  Token Management

   If an access token response includes the "manage" parameter as
   described in Section 3.2.1, the client MAY call this URL to manage
   the access token with any of the actions defined in the following
   sections.  Other actions are undefined by this specification.

   The access token being managed acts as the access element for its own
   management API.  The client MUST present proof of an appropriate key
   along with the access token.

   If the token is sender-constrained (i.e., not a bearer token), it
   MUST be sent with the appropriate binding for the access token
   (Section 7).

   If the token is a bearer token, the client MUST present proof of the
   same key identified in the initial request (Section 2.3) as described
   in Section 8.

   The AS MUST validate the proof and assure that it is associated with
   either the token itself or the client the token was issued to, as
   appropriate for the token's presentation type.

6.1.  Rotating the Access Token

   The client makes an HTTP POST to the token management URI, sending
   the access token in the appropriate header and signing the request
   with the appropriate key.

Richer                  Expires January 26, 2021               [Page 35]
Internet-Draft             transactional-authz                 July 2020

   POST /token/PRY5NM33OM4TB8N6BW7OZB8CDFONP219RP1L HTTP/1.1
   Host: server.example.com
   Authorization: GNAP OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0
   Detached-JWS: eyj0....

   If the token is validated and the key is appropriate for the request,
   the AS will invalidate the current access token associated with this
   URL, if possible, and return a new access token response as described
   in Section 3.2.1.  The value of the access token MUST NOT be the same
   as the current value of the access token used to access the
   management API.  The response MAY include an updated access token
   management URL as well, and if so, the client MUST use this new URL
   to manage the new access token.

{
    "access_token": {
        "value": "FP6A8H6HY37MH13CK76LBZ6Y1UADG6VEUPEER5H2",
        "proof": "bearer",
        "manage": "https://server.example.com/token/PRY5NM33OM4TB8N6BW7OZB8CDFONP219RP1L",
        "resources": [
            {
                "type": "photo-api",
                "actions": [
                    "read",
                    "write",
                    "dolphin"
                ],
                "locations": [
                    "https://server.example.net/",
                    "https://resource.local/other"
                ],
                "datatypes": [
                    "metadata",
                    "images"
                ]
            },
            "read", "dolphin-metadata"
        ]
    }
}

6.2.  Revoking the Access Token

   The client makes an HTTP DELETE request to the token management URI,
   signing the request with its key.

Richer                  Expires January 26, 2021               [Page 36]
Internet-Draft             transactional-authz                 July 2020

   DELETE /token/PRY5NM33OM4TB8N6BW7OZB8CDFONP219RP1L HTTP/1.1
   Host: server.example.com
   Authorization: GNAP OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0
   Detached-JWS: eyj0....

   If the token was issued to the client identified by the key, the AS
   will invalidate the current access token associated with this URL, if
   possible, and return an HTTP 204 response code.

   204 No Content

7.  Sending Access Tokens

   The method used to send an access token depends on the value of the
   "proof" parameter in the access token response (Section 3.2.1).

   If this value is "bearer", the access token is sent using the HTTP
   Header method defined in [RFC6750].

   Authorization: Bearer OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0

   If the "proof" value is any other string, the access token is sent
   using the HTTP authorization scheme "GNAP" along with a key proof as
   described in Section 8 for the key bound to the access token.  For
   example, a "jwsd"-bound access token is sent as follows:

   Authorization: GNAP OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0
   Detached-JWS: eyj0....

   [[ Editor's note: I don't actually like the idea of using only one
   header type for differently-bound access tokens, but instead these
   values should somehow reflect the key binding types.  Maybe there can
   be multiple fields after the "GNAP" keyword using structured headers?
   Or a set of derived headers like GNAP-mtls?  This might also be
   better as a separate specification, like OAuth 2. ]]

8.  Binding Keys

   Any keys presented by the RC to the AS or RS MUST be validated as
   part of the request in which they are presented.  The type of binding
   used is indicated by the proof parameter of the key section in the
   initial request Section 2.3.  Values defined by this specification
   are as follows:

   jwsd  A detached JWS signature header

   jws  Attached JWS payload

Richer                  Expires January 26, 2021               [Page 37]
Internet-Draft             transactional-authz                 July 2020

   mtls  Mutual TLS certificate verification

   dpop  OAuth DPoP key proof header

   httpsig  HTTP Signing signature header

   oauthpop  OAuth PoP key proof authentication header

   Additional values can be defined by [[ a registry TBD ]].

   The keys presented by the RC in the requestSection 2 MUST be proved
   in all continuation requestsSection 5 and token management requests
   Section 6.  The AS MUST validate all keys presented by the RC
   (Section 2.3) or referenced in an ongoing transaction at each call.

8.1.  Detached JWS

   This method is indicated by "jwsd" in the "proof" field.  To sign a
   request, the RC takes the serialized body of the request and signs it
   using detached JWS [RFC7797].  The header of the JWS MUST contain the
   kid field of the key bound to this RC for this request.  The JWS
   header MUST contain an alg field appropriate for the key identified
   by kid and MUST NOT be none.

   The RC presents the signature in the Detached-JWS HTTP Header field.
   [Editor's Note: this is a custom header field, do we need this?]

Richer                  Expires January 26, 2021               [Page 38]
Internet-Draft             transactional-authz                 July 2020

  POST /tx HTTP/1.1
  Host: server.example.com
  Content-Type: application/json
  Detached-JWS: eyJiNjQiOmZhbHNlLCJhbGciOiJSUzI1NiIsImtpZCI6Inh5ei0xIn0.
    .Y287HMtaY0EegEjoTd_04a4GC6qV48GgVbGKOhHdJnDtD0VuUlVjLfwne8AuUY3U7e8
    9zUWwXLnAYK_BiS84M8EsrFvmv8yDLWzqveeIpcN5_ysveQnYt9Dqi32w6IOtAywkNUD
    ZeJEdc3z5s9Ei8qrYFN2fxcu28YS4e8e_cHTK57003WJu-wFn2TJUmAbHuqvUsyTb-nz
    YOKxuCKlqQItJF7E-cwSb_xULu-3f77BEU_vGbNYo5ZBa2B7UHO-kWNMSgbW2yeNNLbL
    C18Kv80GF22Y7SbZt0e2TwnR2Aa2zksuUbntQ5c7a1-gxtnXzuIKa34OekrnyqE1hmVW
    peQ

  {
      "display": {
          "name": "My Client Display Name",
          "uri": "https://example.net/client"
      },
      "resources": [
          "dolphin-metadata"
      ],
      "interact": {
          "redirect": true,
          "callback": {
              "uri": "https://client.foo",
              "nonce": "VJLO6A4CAYLBXHTR0KRO"
          }
      },
      "key": {
          "proof": "jwsd",
          "jwk": {
                      "kty": "RSA",
                      "e": "AQAB",
                      "kid": "xyz-1",
                      "alg": "RS256",
                      "n": "kOB5rR4Jv0GMeLaY6_It_r3ORwdf8ci_JtffXyaSx8
  xYJCNaOKNJn_Oz0YhdHbXTeWO5AoyspDWJbN5w_7bdWDxgpD-y6jnD1u9YhBOCWObNPF
  vpkTM8LC7SdXGRKx2k8Me2r_GssYlyRpqvpBlY5-ejCywKRBfctRcnhTTGNztbbDBUyD
  SWmFMVCHe5mXT4cL0BwrZC6S-uu-LAx06aKwQOPwYOGOslK8WPm1yGdkaA1uF_FpS6LS
  63WYPHi_Ap2B7_8Wbw4ttzbMS_doJvuDagW8A1Ip3fXFAHtRAcKw7rdI4_Xln66hJxFe
  kpdfWdiPQddQ6Y1cK2U3obvUg7w"
          }
      }
  }

   When the AS receives the Detached-JWS header, it MUST parse its
   contents as a detached JWS object.  The HTTP Body is used as the
   payload for purposes of validating the JWS, with no transformations.

Richer                  Expires January 26, 2021               [Page 39]
Internet-Draft             transactional-authz                 July 2020

   [[ Editor's note: this is a potentially fragile signature mechanism
   but it's simple to calculate and useful for body-driven requests,
   like the client to the AS.  We might want to remove this in favor of
   general-purpose HTTP signing. ]]

8.2.  Attached JWS

   This method is indicated by "jws" in the "proof" field.  To sign a
   request, the RC takes the serialized body of the request JSON and
   signs it using JWS [RFC7515].  The header of the JWS MUST contain the
   kid field of the key bound to this RC during this request.  The JWS
   header MUST contain an alg field appropriate for the key identified
   by kid and MUST NOT be none.

   The RC presents the JWS as the body of the request along with a
   content type of "application/jose".  The AS MUST extract the payload
   of the JWS and treat it as the request body for further processing.

   POST /transaction HTTP/1.1
   Host: server.example.com
   Content-Type: application/jose

   eyJiNjQiOmZhbHNlLCJhbGciOiJSUzI1NiIsImtpZCI6Inh5ei0xIn0.ewogICAgIm
   NsaWVudCI6IHsKICAgICAgICAibmFtZSI6ICJNeSBDbGllbnQgRGlzcGxheSBOYW1l
   IiwKICAgICAgICAidXJpIjogImh0dHBzOi8vZXhhbXBsZS5uZXQvY2xpZW50IgogIC
   AgfSwKICAgICJyZXNvdXJjZXMiOiBbCiAgICAgICAgImRvbHBoaW4tbWV0YWRhdGEi
   CiAgICBdLAogICAgImludGVyYWN0IjogewogICAgICAgICJyZWRpcmVjdCI6IHRydW
   UsCiAgICAgICAgImNhbGxiYWNrIjogewogICAgCQkidXJpIjogImh0dHBzOi8vY2xp
   ZW50LmZvbyIsCiAgICAJCSJub25jZSI6ICJWSkxPNkE0Q0FZTEJYSFRSMEtSTyIKIC
   AgIAl9CiAgICB9LAogICAgImtleXMiOiB7CgkJInByb29mIjogImp3c2QiLAogICAg
   ICAgICJqd2tzIjogewogICAgICAgICAgICAia2V5cyI6IFsKICAgICAgICAgICAgIC
   AgIHsKICAgICAgICAgICAgICAgICAgICAia3R5IjogIlJTQSIsCiAgICAgICAgICAg
   ICAgICAgICAgImUiOiAiQVFBQiIsCiAgICAgICAgICAgICAgICAgICAgImtpZCI6IC
   J4eXotMSIsCiAgICAgICAgICAgICAgICAgICAgImFsZyI6ICJSUzI1NiIsCiAgICAg
   ICAgICAgICAgICAgICAgIm4iOiAia09CNXJSNEp2MEdNZUxhWTZfSXRfcjNPUndkZj
   hjaV9KdGZmWHlhU3g4eFlKQ0NOYU9LTkpuX096MFloZEhiWFRlV081QW95c3BEV0pi
   TjV3XzdiZFdEeGdwRC15NmpuRDF1OVloQk9DV09iTlBGdnBrVE04TEM3U2RYR1JLeD
   JrOE1lMnJfR3NzWWx5UnBxdnBCbFk1LWVqQ3l3S1JCZmN0UmNuaFRUR056dGJiREJV
   eURTV21GTVZDSGU1bVhUNGNMMEJ3clpDNlMtdXUtTEF4MDZhS3dRT1B3WU9HT3NsSz
   hXUG0xeUdka2FBMXVGX0ZwUzZMUzYzV1lQSGlfQXAyQjdfOFdidzR0dHpiTVNfZG9K
   dnVEYWdXOEExSXAzZlhGQUh0UkFjS3c3cmRJNF9YbG42NmhKeEZla3BkZldkaVBRZG
   RRNlkxY0syVTNvYnZVZzd3IgogICAgICAgICAgICAgICAgfQogICAgICAgICAgICBd
   CiAgICAgICAgfQogICAgfQp9.Y287HMtaY0EegEjoTd_04a4GC6qV48GgVbGKOhHdJ
   nDtD0VuUlVjLfwne8AuUY3U7e89zUWwXLnAYK_BiS84M8EsrFvmv8yDLWzqveeIpcN
   5_ysveQnYt9Dqi32w6IOtAywkNUDZeJEdc3z5s9Ei8qrYFN2fxcu28YS4e8e_cHTK5
   7003WJu-wFn2TJUmAbHuqvUsyTb-nzYOKxuCKlqQItJF7E-cwSb_xULu-3f77BEU_v
   GbNYo5ZBa2B7UHO-kWNMSgbW2yeNNLbLC18Kv80GF22Y7SbZt0e2TwnR2Aa2zksuUb
   ntQ5c7a1-gxtnXzuIKa34OekrnyqE1hmVWpeQ

Richer                  Expires January 26, 2021               [Page 40]
Internet-Draft             transactional-authz                 July 2020

   [[ Editor's note: A downside to this method is that it requires the
   content type to be something other than application/json, and it
   doesn't work against an RS without additional profiling since it
   requires things to be sent in the body.  Additionally it is
   potentially fragile like a detached JWS since a multi-tier system
   could parse the payload and pass it downstream with potential
   transformations. ]]

8.3.  Mutual TLS

   This method is indicated by "mtls" in the "proof" field.  The RC
   presents its client certificate during TLS negotiation with the
   server (either AS or RS).  The AS or RS takes the thumbprint of the
   client certificate presented during mutual TLS negotiation and
   compares that thumbprint to the thumbprint presented by the RC
   application as described in [RFC8705] section 3.

Client?AS

POST /transaction HTTP/1.1
Host: server.example.com
Content-Type: application/json
SSL_CLIENT_CERT: MIIEHDCCAwSgAwIBAgIBATANBgkqhkiG9w0BAQsFADCBmjE3MDUGA1UEAwwuQmVz
 cG9rZSBFbmdpbmVlcmluZyBSb290IENlcnRpZmljYXRlIEF1dGhvcml0eTELMAkG
 A1UECAwCTUExCzAJBgNVBAYTAlVTMRkwFwYJKoZIhvcNAQkBFgpjYUBic3BrLmlv
 MRwwGgYDVQQKDBNCZXNwb2tlIEVuZ2luZWVyaW5nMQwwCgYDVQQLDANNVEkwHhcN
 MTkwNDEwMjE0MDI5WhcNMjQwNDA4MjE0MDI5WjB8MRIwEAYDVQQDDAlsb2NhbGhv
 c3QxCzAJBgNVBAgMAk1BMQswCQYDVQQGEwJVUzEgMB4GCSqGSIb3DQEJARYRdGxz
 Y2xpZW50QGJzcGsuaW8xHDAaBgNVBAoME0Jlc3Bva2UgRW5naW5lZXJpbmcxDDAK
 BgNVBAsMA01USTCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBAMmaXQHb
 s/wc1RpsQ6Orzf6rN+q2ijaZbQxD8oi+XaaN0P/gnE13JqQduvdq77OmJ4bQLokq
 sd0BexnI07Njsl8nkDDYpe8rNve5TjyUDCfbwgS7U1CluYenXmNQbaYNDOmCdHww
 UjV4kKREg6DGAx22Oq7+VHPTeeFgyw4kQgWRSfDENWY3KUXJlb/vKR6lQ+aOJytk
 vj8kVZQtWupPbvwoJe0na/ISNAOhL74w20DWWoDKoNltXsEtflNljVoi5nqsmZQc
 jfjt6LO0T7O1OX3Cwu2xWx8KZ3n/2ocuRqKEJHqUGfeDtuQNt6Jz79v/OTr8puLW
 aD+uyk6NbtGjoQsCAwEAAaOBiTCBhjAJBgNVHRMEAjAAMAsGA1UdDwQEAwIF4DBs
 BgNVHREEZTBjgglsb2NhbGhvc3SCD3Rsc2NsaWVudC5sb2NhbIcEwKgBBIERdGxz
 Y2xpZW50QGJzcGsuaW+GF2h0dHA6Ly90bHNjbGllbnQubG9jYWwvhhNzc2g6dGxz
 Y2xpZW50LmxvY2FsMA0GCSqGSIb3DQEBCwUAA4IBAQCKKv8WlLrT4Z5NazaUrYtl
 TF+2v0tvZBQ7qzJQjlOqAcvxry/d2zyhiRCRS/v318YCJBEv4Iq2W3I3JMMyAYEe
 2573HzT7rH3xQP12yZyRQnetdiVM1Z1KaXwfrPDLs72hUeELtxIcfZ0M085jLboX
 hufHI6kqm3NCyCCTihe2ck5RmCc5l2KBO/vAHF0ihhFOOOby1v6qbPHQcxAU6rEb
 907/p6BW/LV1NCgYB1QtFSfGxowqb9FRIMD2kvMSmO0EMxgwZ6k6spa+jk0IsI3k
 lwLW9b+Tfn/daUbIDctxeJneq2anQyU2znBgQl6KILDSF4eaOqlBut/KNZHHazJh

{
    "client": {
        "name": "My Client Display Name",

Richer                  Expires January 26, 2021               [Page 41]
Internet-Draft             transactional-authz                 July 2020

        "uri": "https://example.net/client"
    },
    "resources": [
        "dolphin-metadata"
    ],
    "interact": {
        "redirect": true,
        "callback": {
            "uri": "https://client.foo",
            "nonce": "VJLO6A4CAYLBXHTR0KRO"
        }
    },
    "key": {
        "proof": "mtls",
        "cert": "MIIEHDCCAwSgAwIBAgIBATANBgkqhkiG9w0BAQsFADCBmjE3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"
    }
}

8.4.  DPoP

   This method is indicated by "dpop" in the "proof" field.  The RC
   creates a DPoP signature header as described in [I-D.ietf-oauth-dpop]
   section 2.

Richer                  Expires January 26, 2021               [Page 42]
Internet-Draft             transactional-authz                 July 2020

POST /transaction HTTP/1.1
Host: server.example.com
Content-Type: application/json
DPoP: eyJ0eXAiOiJkcG9wK2p3dCIsImFsZyI6IlJTMjU2IiwiandrIjp7Imt0eSI6Il
JTQSIsImUiOiJBUUFCIiwia2lkIjoieHl6LWNsaWVudCIsImFsZyI6IlJTMjU2Iiwibi
I6Inp3Q1RfM2J4LWdsYmJIcmhlWXBZcFJXaVk5SS1uRWFNUnBablJySWpDczZiX2VteV
RrQmtEREVqU3lzaTM4T0M3M2hqMS1XZ3hjUGRLTkdaeUlvSDNRWmVuMU1LeXloUXBMSk
cxLW9MTkxxbTdwWFh0ZFl6U2RDOU8zLW9peXk4eWtPNFlVeU5aclJSZlBjaWhkUUNiT1
9PQzhRdWdtZzlyZ05ET1NxcHBkYU5lYXMxb3Y5UHhZdnhxcnoxLThIYTdna0QwMFlFQ1
hIYUIwNXVNYVVhZEhxLU9fV0l2WVhpY2c2STVqNlM0NFZOVTY1VkJ3dS1BbHluVHhRZE
1BV1AzYll4VlZ5NnAzLTdlVEpva3ZqWVRGcWdEVkRaOGxVWGJyNXlDVG5SaG5oSmd2Zj
NWakRfbWFsTmU4LXRPcUs1T1NEbEhUeTZnRDlOcWRHQ20tUG0zUSJ9fQ.eyJodHRwX21
ldGhvZCI6IlBPU1QiLCJodHRwX3VyaSI6Imh0dHA6XC9cL2hvc3QuZG9ja2VyLmludGV
ybmFsOjk4MzRcL2FwaVwvYXNcL3RyYW5zYWN0aW9uIiwiaWF0IjoxNTcyNjQyNjEzLCJ
qdGkiOiJIam9IcmpnbTJ5QjR4N2pBNXl5RyJ9.aUhftvfw2NoW3M7durkopReTvONng1
fOzbWjAlKNSLL0qIwDgfG39XUyNvwQ23OBIwe6IuvTQ2UBBPklPAfJhDTKd8KHEAfidN
B-LzUOzhDetLg30yLFzIpcEBMLCjb0TEsmXadvxuNkEzFRL-Q-QCg0AXSF1h57eAqZV8
SYF4CQK9OUV6fIWwxLDd3cVTx83MgyCNnvFlG_HDyim1Xx-rxV4ePd1vgDeRubFb6QWj
iKEO7vj1APv32dsux67gZYiUpjm0wEZprjlG0a07R984KLeK1XPjXgViEwEdlirUmpVy
T9tyEYqGrTfm5uautELgMls9sgSyE929woZ59elg

{
    "client": {
        "name": "My Client Display Name",
        "uri": "https://example.net/client"
    },
    "resources": [
        "dolphin-metadata"
    ],
    "interact": {
        "redirect": true,
        "callback": {
            "uri": "https://client.foo",
            "nonce": "VJLO6A4CAYLBXHTR0KRO"
        }
    },
    "key": {
        "proof": "dpop",
        "jwk": {
                    "kty": "RSA",
                    "e": "AQAB",
                    "kid": "xyz-1",
                    "alg": "RS256",
                    "n": "kOB5rR4Jv0GMeLaY6_It_r3ORwdf8ci_JtffXyaSx8xYJCCNaOKNJn_Oz0YhdHbXTeWO5AoyspDWJbN5w_7bdWDxgpD-y6jnD1u9YhBOCWObNPFvpkTM8LC7SdXGRKx2k8Me2r_GssYlyRpqvpBlY5-ejCywKRBfctRcnhTTGNztbbDBUyDSWmFMVCHe5mXT4cL0BwrZC6S-uu-LAx06aKwQOPwYOGOslK8WPm1yGdkaA1uF_FpS6LS63WYPHi_Ap2B7_8Wbw4ttzbMS_doJvuDagW8A1Ip3fXFAHtRAcKw7rdI4_Xln66hJxFekpdfWdiPQddQ6Y1cK2U3obvUg7w"
        }
    }
}

Richer                  Expires January 26, 2021               [Page 43]
Internet-Draft             transactional-authz                 July 2020

   [[ Editor's note: this method requires duplication of the key in the
   header and the request body, which is redundant and potentially
   awkward. ]]

8.5.  HTTP Signing

   This method is indicated by "httpsig" in the "proof" field.  The RC
   creates an HTTP Signature header as described in
   [I-D.ietf-httpbis-message-signatures] section 4.  The RC MUST
   calculate and present the Digest header as defined in [RFC3230].

Richer                  Expires January 26, 2021               [Page 44]
Internet-Draft             transactional-authz                 July 2020

   POST /transaction HTTP/1.1
   Host: server.example.com
   Content-Type: application/json
   Content-Length: 716
   Signature: keyId="xyz-client", algorithm="rsa-sha256",
    headers="(request-target) digest content-length",
    signature="TkehmgK7GD/z4jGkmcHS67cjVRgm3zVQNlNrrXW32Wv7d
   u0VNEIVI/dMhe0WlHC93NP3ms91i2WOW5r5B6qow6TNx/82/6W84p5jqF
   YuYfTkKYZ69GbfqXkYV9gaT++dl5kvZQjVk+KZT1dzpAzv8hdk9nO87Xi
   rj7qe2mdAGE1LLc3YvXwNxuCQh82sa5rXHqtNT1077fiDvSVYeced0UEm
   rWwErVgr7sijtbTohC4FJLuJ0nG/KJUcIG/FTchW9rd6dHoBnY43+3Dzj
   CIthXpdH5u4VX3TBe6GJDO6Mkzc6vB+67OWzPwhYTplUiFFV6UZCsDEeu
   Sa/Ue1yLEAMg=="]}
   Digest: SHA=oZz2O3kg5SEFAhmr0xEBbc4jEfo=

   {
       "client": {
           "name": "My Client Display Name",
           "uri": "https://example.net/client"
       },
       "resources": [
           "dolphin-metadata"
       ],
       "interact": {
           "redirect": true,
           "callback": {
               "uri": "https://client.foo",
               "nonce": "VJLO6A4CAYLBXHTR0KRO"
           }
       },
       "key": {
           "proof": "httpsig",
           "jwk": {
                       "kty": "RSA",
                       "e": "AQAB",
                       "kid": "xyz-1",
                       "alg": "RS256",
                       "n": "kOB5rR4Jv0GMeLaY6_It_r3ORwdf8ci_J
   tffXyaSx8xYJCCNaOKNJn_Oz0YhdHbXTeWO5AoyspDWJbN5w_7bdWDxgpD-
   y6jnD1u9YhBOCWObNPFvpkTM8LC7SdXGRKx2k8Me2r_GssYlyRpqvpBlY5-
   ejCywKRBfctRcnhTTGNztbbDBUyDSWmFMVCHe5mXT4cL0BwrZC6S-uu-LAx
   06aKwQOPwYOGOslK8WPm1yGdkaA1uF_FpS6LS63WYPHi_Ap2B7_8Wbw4ttz
   bMS_doJvuDagW8A1Ip3fXFAHtRAcKw7rdI4_Xln66hJxFekpdfWdiPQddQ6
   Y1cK2U3obvUg7w"
           }
       }
   }

Richer                  Expires January 26, 2021               [Page 45]
Internet-Draft             transactional-authz                 July 2020

8.6.  OAuth PoP

   This method is indicated by "oauthpop" in the "proof" field.  The RC
   creates an HTTP Authorization PoP header as described in
   [I-D.ietf-oauth-signed-http-request] section 4, with the following
   additional requirements:

   o  The at (access token) field MUST be omitted [note: this is in
      contrast to the requirements in the existing spec]

   o  The b (body hash) field MUST be calculated and supplied

   POST /transaction HTTP/1.1
   Host: server.example.com
   Content-Type: application/json
   PoP: eyJhbGciOiJSUzI1NiIsImp3ayI6eyJrdHkiOiJSU0EiLCJlIjoi
   QVFBQiIsImtpZCI6Inh5ei1jbGllbnQiLCJhbGciOiJSUzI1NiIsIm4iO
   iJ6d0NUXzNieC1nbGJiSHJoZVlwWXBSV2lZOUktbkVhTVJwWm5ScklqQ3
   M2Yl9lbXlUa0JrRERFalN5c2kzOE9DNzNoajEtV2d4Y1BkS05HWnlJb0g
   zUVplbjFNS3l5aFFwTEpHMS1vTE5McW03cFhYdGRZelNkQzlPMy1vaXl5
   OHlrTzRZVXlOWnJSUmZQY2loZFFDYk9fT0M4UXVnbWc5cmdORE9TcXBwZ
   GFOZWFzMW92OVB4WXZ4cXJ6MS04SGE3Z2tEMDBZRUNYSGFCMDV1TWFVYW
   RIcS1PX1dJdllYaWNnNkk1ajZTNDRWTlU2NVZCd3UtQWx5blR4UWRNQVd
   QM2JZeFZWeTZwMy03ZVRKb2t2allURnFnRFZEWjhsVVhicjV5Q1RuUmhu
   aEpndmYzVmpEX21hbE5lOC10T3FLNU9TRGxIVHk2Z0Q5TnFkR0NtLVBtM
   1EifX0.eyJwIjoiXC9hcGlcL2FzXC90cmFuc2FjdGlvbiIsImIiOiJxa0
   lPYkdOeERhZVBTZnc3NnFjamtqSXNFRmxDb3g5bTU5NFM0M0RkU0xBIiw
   idSI6Imhvc3QuZG9ja2VyLmludGVybmFsIiwiaCI6W1siQWNjZXB0Iiwi
   Q29udGVudC1UeXBlIiwiQ29udGVudC1MZW5ndGgiXSwiVjQ2OUhFWGx6S
   k9kQTZmQU5oMmpKdFhTd3pjSGRqMUloOGk5M0h3bEVHYyJdLCJtIjoiUE
   9TVCIsInRzIjoxNTcyNjQyNjEwfQ.xyQ47qy8bu4fyK1T3Ru1Sway8wp6
   5rfAKnTQQU92AUUU07I2iKoBL2tipBcNCC5zLH5j_WUyjlN15oi_lLHym
   fPdzihtt8_Jibjfjib5J15UlifakjQ0rHX04tPal9PvcjwnyZHFcKn-So
   Y3wsARn-gGwxpzbsPhiKQP70d2eG0CYQMA6rTLslT7GgdQheelhVFW29i
   27NcvqtkJmiAG6Swrq4uUgCY3zRotROkJ13qo86t2DXklV-eES4-2dCxf
   cWFkzBAr6oC4Qp7HnY_5UT6IWkRJt3efwYprWcYouOVjtRan3kEtWkaWr
   G0J4bPVnTI5St9hJYvvh7FE8JirIg

   {
       "client": {
           "name": "My Client Display Name",
           "uri": "https://example.net/client"
       },
       "resources": [
           "dolphin-metadata"
       ],
       "interact": {
           "redirect": true,

Richer                  Expires January 26, 2021               [Page 46]
Internet-Draft             transactional-authz                 July 2020

           "callback": {
               "uri": "https://client.foo",
               "nonce": "VJLO6A4CAYLBXHTR0KRO"
           }
       },
       "key": {
           "proof": "oauthpop",
           "jwk": {
                       "kty": "RSA",
                       "e": "AQAB",
                       "kid": "xyz-1",
                       "alg": "RS256",
                       "n": "kOB5rR4Jv0GMeLaY6_It_r3ORwdf8ci_J
   tffXyaSx8xYJCCNaOKNJn_Oz0YhdHbXTeWO5AoyspDWJbN5w_7bdWDxgpD-
   y6jnD1u9YhBOCWObNPFvpkTM8LC7SdXGRKx2k8Me2r_GssYlyRpqvpBlY5-
   ejCywKRBfctRcnhTTGNztbbDBUyDSWmFMVCHe5mXT4cL0BwrZC6S-uu-LAx
   06aKwQOPwYOGOslK8WPm1yGdkaA1uF_FpS6LS63WYPHi_Ap2B7_8Wbw4ttz
   bMS_doJvuDagW8A1Ip3fXFAHtRAcKw7rdI4_Xln66hJxFekpdfWdiPQddQ6
   Y1cK2U3obvUg7w"
           }
       }
   }

9.  Discovery

   By design, the protocol minimizes the need for any pre-flight
   discovery.  To begin a request, the RC only needs to know the
   endpoint of the AS and which keys it will use to sign the request.
   Everything else can be negotiated dynamically in the course of the
   protocol.

   However, the AS can have limits on its allowed functionality.  If the
   RC wants to optimize its calls to the AS before making a request, it
   MAY send an HTTP OPTIONS request to the transaction endpoint to
   retrieve the server's discovery information.  The AS MUST respond
   with a JSON document containing the following information:

   grant_request_endpoint  REQUIRED.  The full URL of the AS's grant
      request endpoint.  This MUST match the URL the RC used to make the
      discovery request.

   capabilities  OPTIONAL.  A list of the AS's capabilities.  The values
      of this result MAY be used by the RC in the capabilities section
      (Section 2.7) of the request.

   interaction_methods  OPTIONAL.  A list of the AS's interaction
      methods.  The values of this list correspond to the possible
      fields in the interaction section (Section 2.5) of the request.

Richer                  Expires January 26, 2021               [Page 47]
Internet-Draft             transactional-authz                 July 2020

   key_proofs  OPTIONAL.  A list of the AS's supported key proofing
      mechanisms.  The values of this list correspond to possible values
      of the "proof" field of the key section (Section 2.3) of the
      request.

   sub-ids  OPTIONAL.  A list of the AS's supported identifiers.  The
      values of this list correspond to possible values of the subject
      identifier section (Section 2.2) of the request.

   assertions  OPTIONAL.  A list of the AS's supported assertion
      formats.  The values of this list correspond to possible values of
      the subject assertion section (Section 2.2) of the request.

   The information returned from this method is for optimization
   purposes only.  The AS MAY deny any request, or any portion of a
   request, even if it lists a capability as supported.  For example, a
   given client can be registered with the "mtls" key proofing
   mechanism, but the AS also returns other proofing methods, then the
   AS will deny a request from that client using a different proofing
   mechanism.

10.  Resource Servers

   In some deployments, a resource server will need to be able to call
   the AS for a number of functions.

   [[ Editor's note: This section is for discussion of possible advanced
   functionality.  It seems like it should be a separate document or set
   of documents, and it's not even close to being well-baked.  This also
   adds additional endpoints to the AS, as this is separate from the
   token request process, and therefore would require RS-facing
   discovery or configuration information to make it work.  Also-also,
   it does presume the RS can sign requests in the same way that a
   client does, but hopefully we can be more consistent with this than
   RFC7662 was able to do. ]]

10.1.  Introspecting a Token

   When the RS receives an access token, it can call the introspection
   endpoint at the AS to get token information. [[ Editor's note: this
   isn't super different from the token management URIs, but the RS has
   no way to get that URI, and it's bound to different keys. ]]

   The RS signs the request with its own key and sends the access token
   as the body of the request.

Richer                  Expires January 26, 2021               [Page 48]
Internet-Draft             transactional-authz                 July 2020

   POST /introspect HTTP/1.1
   Host: server.example.com
   Content-type: application/json
   Detached-JWS: ejy0...

   {
       "access_token": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
   }

   The AS responds with a data structure describing the token's current
   state and any information the RS would need to validate the token's
   presentation, such as its intended proofing mechanism and key
   material.

   Content-type: application/json

   {
       "active": true,
       "resources": [
           "dolphin-metadata", "some other thing"
       ],
       "resources": [
           "dolphin-metadata", "some other thing"
       ],
       "proof": "httpsig",
       "key": {
           "proof": "jwsd",
           "jwk": {
                       "kty": "RSA",
                       "e": "AQAB",
                       "kid": "xyz-1",
                       "alg": "RS256",
                       "n": "kOB5rR4Jv0GMeL...."
           }
       }
   }

10.2.  Deriving a downstream token

   If the RS needs to derive a token from one presented to it, it can
   request one from the AS by making a token request as described in
   Section 2 and presenting the existing access token's value in the
   "existing_access_token" field.

   The RS MUST identify itself with its own key and sign the request.

   [[ Editor's note: this is similar to but based on the access token
   and not the grant.  The fact that the keys presented are not the ones

Richer                  Expires January 26, 2021               [Page 49]
Internet-Draft             transactional-authz                 July 2020

   used for the access token should indicate that it's a different party
   and a different kind of request. ]]

 POST /tx HTTP/1.1
 Host: server.example.com
 Content-type: application/json
 Detached-JWS: ejy0...

 {
     "resources": [
         {
             "actions": [
                 "read",
                 "write",
                 "dolphin"
             ],
             "locations": [
                 "https://server.example.net/",
                 "https://resource.local/other"
             ],
             "datatypes": [
                 "metadata",
                 "images"
             ]
         },
         "dolphin-metadata"
     ],
     "key": "7C7C4AZ9KHRS6X63AJAO",
     "existing_access_token": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0"
 }

   The AS responds with a token as described in Section 3.

10.3.  Registering a Resource Handle

   If the RS needs to, it can post a set of resources as described in
   Section 2.1.1 to the AS's resource registration endpoint.

   The RS MUST identify itself with its own key and sign the request.

Richer                  Expires January 26, 2021               [Page 50]
Internet-Draft             transactional-authz                 July 2020

   POST /resource HTTP/1.1
   Host: server.example.com
   Content-type: application/json
   Detached-JWS: ejy0...

   {
       "resources": [
           {
               "actions": [
                   "read",
                   "write",
                   "dolphin"
               ],
               "locations": [
                   "https://server.example.net/",
                   "https://resource.local/other"
               ],
               "datatypes": [
                   "metadata",
                   "images"
               ]
           },
           "dolphin-metadata"
       ],
       "key": "7C7C4AZ9KHRS6X63AJAO"

   }

   The AS responds with a handle appropriate to represent the resources
   list that the RS presented.

   Content-type: application/json

   {
       "resource_handle": "FWWIKYBQ6U56NL1"
   }

   The RS MAY make this handle available as part of a response to a
   client (Section 10.4) or as documentation to developers.

   [[ Editor's note: It's not an exact match here because the
   "resource_handle" returned now represents a collection of objects
   instead of a single one.  Perhaps we should let this return a list of
   strings instead?  Or use a different syntax than the resource
   request?  Also, this borrows heavily from UMA 2's "distributed
   authorization" model and, like UMA, might be better suited to an
   extension than the core protocol. ]]

Richer                  Expires January 26, 2021               [Page 51]
Internet-Draft             transactional-authz                 July 2020

10.4.  Requesting a Resources Without a Token

   If the client calls an RS without an access token, or with an invalid
   access token, the RS MAY respond to the client with an authentication
   header indicating that GNAP.  The address of the GNAP endpoint MUST
   be sent in the "as_uri" parameter.  The RS MAY additionally return a
   resource reference that the client MAY use in its resource request
   (Section 2.1).  This resource reference handle SHOULD be sufficient
   for at least the action the client was attempting to take at the RS.
   The RS MAY use the dynamic resource handle request (Section 10.3) to
   register a new resource handle, or use a handle that has been pre-
   configured to represent what the AS is protecting.  The content of
   this handle is opaque to the RS and the client.

WWW-Authenticate: GNAP as_uri=http://server.example/transaction,resource=FWWIKYBQ6U56NL1

   The client then makes a call to the "as_uri" as described in
   Section 2, with the value of "resource" as one of the members of a
   "resources" array Section 2.1.1.  The client MAY request additional
   resources and other information, and MAY request multiple access
   tokens.

   [[ Editor's note: this borrows heavily from UMA 2's "distributed
   authorization" model and, like UMA, might be better suited to an
   extension than the core protocol. ]]

11.  Acknowledgements

   The author would like to thank the feedback of the GNAP working
   group.

12.  IANA Considerations

   [[ TBD: There are a lot of items in the document that are expandable
   through the use of value registries. ]]

13.  Security Considerations

   [[ TBD: There are a lot of security considerations to add. ]]

   All requests have to be over TLS or equivalent.  Many handles act as
   shared secrets, though they can be combined with a requirement to
   provide proof of a key as well.

Richer                  Expires January 26, 2021               [Page 52]
Internet-Draft             transactional-authz                 July 2020

14.  Privacy Considerations

   [[ TBD: There are a lot of privacy considerations to add. ]]

   Handles are passed between parties and therefore should not contain
   any private data.

   When user information is passed to the client, the AS needs to make
   sure that it has the permission to do so.

15.  Normative References

   [BCP195]   Sheffer, Y., Holz, R., and P. Saint-Andre,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
              2015, <http://www.rfc-editor.org/info/bcp195>.

   [I-D.ietf-httpbis-message-signatures]
              Backman, A., Richer, J., and M. Sporny, "Signing HTTP
              Messages", draft-ietf-httpbis-message-signatures-00 (work
              in progress), April 2020.

   [I-D.ietf-oauth-dpop]
              Fett, D., Campbell, B., Bradley, J., Lodderstedt, T.,
              Jones, M., and D. Waite, "OAuth 2.0 Demonstration of
              Proof-of-Possession at the Application Layer (DPoP)",
              draft-ietf-oauth-dpop-01 (work in progress), May 2020.

   [I-D.ietf-oauth-signed-http-request]
              Richer, J., Bradley, J., and H. Tschofenig, "A Method for
              Signing HTTP Requests for OAuth", draft-ietf-oauth-signed-
              http-request-03 (work in progress), August 2016.

   [I-D.ietf-secevent-subject-identifiers]
              Backman, A. and M. Scurtescu, "Subject Identifiers for
              Security Event Tokens", draft-ietf-secevent-subject-
              identifiers-05 (work in progress), July 2019.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC3230]  Mogul, J. and A. Van Hoff, "Instance Digests in HTTP",
              RFC 3230, DOI 10.17487/RFC3230, January 2002,
              <https://www.rfc-editor.org/info/rfc3230>.

Richer                  Expires January 26, 2021               [Page 53]
Internet-Draft             transactional-authz                 July 2020

   [RFC6750]  Jones, M. and D. Hardt, "The OAuth 2.0 Authorization
              Framework: Bearer Token Usage", RFC 6750,
              DOI 10.17487/RFC6750, October 2012,
              <https://www.rfc-editor.org/info/rfc6750>.

   [RFC7515]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web
              Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
              2015, <https://www.rfc-editor.org/info/rfc7515>.

   [RFC7797]  Jones, M., "JSON Web Signature (JWS) Unencoded Payload
              Option", RFC 7797, DOI 10.17487/RFC7797, February 2016,
              <https://www.rfc-editor.org/info/rfc7797>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8259]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", STD 90, RFC 8259,
              DOI 10.17487/RFC8259, December 2017,
              <https://www.rfc-editor.org/info/rfc8259>.

   [RFC8705]  Campbell, B., Bradley, J., Sakimura, N., and T.
              Lodderstedt, "OAuth 2.0 Mutual-TLS Client Authentication
              and Certificate-Bound Access Tokens", RFC 8705,
              DOI 10.17487/RFC8705, February 2020,
              <https://www.rfc-editor.org/info/rfc8705>.

Appendix A.  Document History

   -09

   o  Major document refactoring based on request and response
      capabilities.

   o  Changed from "claims" language to "subject identifier" language.

   o  Added "pushback" interaction capability.

   o  Removed DIDCOMM interaction (better left to extensions).

   o  Excised "transaction" language in favor of "Grant" where
      appropriate.

   o  Added token management URLs.

   o  Added separate grant continuation URL to use continuation handle
      with.

Richer                  Expires January 26, 2021               [Page 54]
Internet-Draft             transactional-authz                 July 2020

   o  Added RS-focused functionality section.

   o  Added notion of extending a grant request based on a previous
      grant.

   -08

   o  Added attached JWS signature method.

   o  Added discovery methods.

   -07

   o  Marked sections as being controlled by a future registry TBD.

   -06

   o  Added multiple resource requests and multiple access token
      response.

   -05

   o  Added "claims" request and response for identity support.

   o  Added "capabilities" request for inline discovery support.

   - 04

   o  Added crypto agility for callback return hash.

   o  Changed "interaction_handle" to "interaction_ref".

   - 03

   o  Removed "state" in favor of "nonce".

   o  Created signed return parameter for front channel return.

   o  Changed "client" section to "display" section, as well as
      associated handle.

   o  Changed "key" to "keys".

   o  Separated key proofing from key presentation.

   o  Separated interaction methods into booleans instead of "type"
      field.

Richer                  Expires January 26, 2021               [Page 55]
Internet-Draft             transactional-authz                 July 2020

   - 02

   o  Minor editorial cleanups.

   - 01

   o  Made JSON multimodal for handle requests.

   o  Major updates to normative language and references throughout
      document.

   o  Allowed interaction to split between how the user gets to the AS
      and how the user gets back.

   - 00

   o  Initial submission.

Appendix B.  Component Data Models

   While different implementations of this protocol will have different
   realizations of all the components and artifacts enumerated here, the
   nature of the protocol implies some common structures and elements
   for certain components.  This appendix seeks to enumerate those
   common elements.

   TBD: Client has keys, allowed requested resources, identifier(s),
   allowed requested subjects, allowed

   TBD: AS has "grant endpoint", interaction endpoints, store of trusted
   client keys, policies

   TBD: Token has RO, user, client, resource list, RS list,

Appendix C.  Example Protocol Flows

   The protocol defined in this specification provides a number of
   features that can be combined to solve many different kinds of
   authentication scenarios.  This section seeks to show examples of how
   the protocol would be applied for different situations.

   Some longer fields, particularly cryptographic information, have been
   truncated for display purposes in these examples.

Richer                  Expires January 26, 2021               [Page 56]
Internet-Draft             transactional-authz                 July 2020

C.1.  Redirect-Based User Interaction

   In this scenario, the user is the RO and has access to a web browser,
   and the client can take front-channel callbacks on the same device as
   the user.  This combination is analogous to the OAuth 2 Authorization
   Code grant type.

   The client initiates the request to the AS.  Here the client
   identifies itself using its public key.

Richer                  Expires January 26, 2021               [Page 57]
Internet-Draft             transactional-authz                 July 2020

   POST /tx HTTP/1.1
   Host: server.example.com
   Content-type: application/json
   Detached-JWS: ejy0...

   {
       "resources": [
           {
               "actions": [
                   "read",
                   "write",
                   "dolphin"
               ],
               "locations": [
                   "https://server.example.net/",
                   "https://resource.local/other"
               ],
               "datatypes": [
                   "metadata",
                   "images"
               ]
           }
       ],
       "key": {
           "proof": "jwsd",
           "jwk": {
               "kty": "RSA",
               "e": "AQAB",
               "kid": "xyz-1",
               "alg": "RS256",
               "n": "kOB5rR4Jv0GMeLaY6_It_r3ORwdf8ci_JtffXyaSx8xY..."
           }
       },
       "interact": {
           "redirect": true,
           "callback": {
               "uri": "https://client.example.net/return/123455",
               "nonce": "LKLTI25DK82FX4T4QFZC"
           }
       }
   }

   The AS processes the request and determines that the RO needs to
   interact.  The AS returns the following response giving the client
   the information it needs to connect.  The AS has also indicated to
   the client that it can use the given key handle to identify itself in
   future calls.

Richer                  Expires January 26, 2021               [Page 58]
Internet-Draft             transactional-authz                 July 2020

Content-type: application/json

{
    "interaction_url": "https://server.example.com/interact/4CF492MLVMSW9MKMXKHQ",
    "server_nonce": "MBDOFXG4Y5CVJCX821LH",
    "continue": {
        "handle": "80UPRY5NM33OMUKMKSKU",
        "uri": "https://server.example.com/continue"
    },
    "key_handle": "7C7C4AZ9KHRS6X63AJAO"
}

   The client saves the response and redirects the user to the
   interaction_url by sending the following HTTP message to the user's
   browser.

   HTTP 302 Found
   Location: https://server.example.com/interact/4CF492MLVMSW9MKMXKHQ

   The user's browser fetches the AS's interaction URL.  The user logs
   in, is identified as the RO for the resource being requested, and
   approves the request.  Since the AS has a callback parameter, the AS
   generates the interaction reference, calculates the hash, and
   redirects the user back to the client with these additional values
   added as query parameters.

HTTP 302 Found
Location: https://client.example.net/return/123455
  ?hash=p28jsq0Y2KK3WS__a42tavNC64ldGTBroywsWxT4md_jZQ1R2HZT8BOWYHcLmObM7XHPAdJzTZMtKBsaraJ64A
  &interact_ref=4IFWWIKYBC2PQ6U56NL1

   The client receives this request from the user's browser.  The client
   ensures that this is the same user that was sent out by validating
   session information and retrieves the stored pending request.  The
   client uses the values in this to validate the hash parameter.  The
   client then calls the continuation URL and presents the handle and
   interaction reference in the request body.  The client signs the
   request as above.

Richer                  Expires January 26, 2021               [Page 59]
Internet-Draft             transactional-authz                 July 2020

   POST /continue HTTP/1.1
   Host: server.example.com
   Content-type: application/json
   Detached-JWS: ejy0...

   {
       "handle": "80UPRY5NM33OMUKMKSKU",
       "interact_ref": "4IFWWIKYBC2PQ6U56NL1"
   }

   The AS retrieves the pending request based on the handle and issues a
   bearer access token and returns this to the client.

Content-type: application/json

{
    "access_token": {
        "value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
        "proof": "bearer",
        "manage": "https://server.example.com/token/PRY5NM33OM4TB8N6BW7OZB8CDFONP219RP1L",
        "resources": [{
            "actions": [
                "read",
                "write",
                "dolphin"
            ],
            "locations": [
                "https://server.example.net/",
                "https://resource.local/other"
            ],
            "datatypes": [
                "metadata",
                "images"
            ]
        }]
    },
    "continue": {
        "handle": "80UPRY5NM33OMUKMKSKU",
        "uri": "https://server.example.com/continue"
    }
}

C.2.  Secondary Device Interaction

   In this scenario, the user does not have access to a web browser on
   the device and must use a secondary device to interact with the AS.

Richer                  Expires January 26, 2021               [Page 60]
Internet-Draft             transactional-authz                 July 2020

   The client can display a user code or a printable QR code.  The
   client prefers a short URL if one is available.

   The client initiates the request to the AS.

   POST /tx HTTP/1.1
   Host: server.example.com
   Content-type: application/json
   Detached-JWS: ejy0...

   {
       "resources": [
           "dolphin-metadata", "some other thing"
       ],
       "key": "7C7C4AZ9KHRS6X63AJAO",
       "interact": {
           "redirect": true,
           "short_redirect": true,
           "user_code": true
       }
   }

   The AS processes this and determines that the RO needs to interact.
   The AS supports both long and short redirect URIs for interaction, so
   it includes both.  Since there is no "callback" the AS does not
   include a nonce, but does include a "wait" parameter on the
   continuation section because it expects the client to poll for
   results.

Content-type: application/json

{
    "interaction_url": "https://server.example.com/interact/4CF492MLVMSW9MKMXKHQ",
    "short_interaction_url": "https://srv.ex/MXKHQ",
    "user_code": {
        "code": "A1BC-3DFF",
        "url": "https://srv.ex/device"
    },
    "continue": {
        "handle": "80UPRY5NM33OMUKMKSKU",
        "uri": "https://server.example.com/continue",
        "wait": 60
    }
}

   The client saves the response and displays the user code visually on
   its screen along with the static device URL.  The client also
   displays the short interaction URL as a QR code to be scanned.  The

Richer                  Expires January 26, 2021               [Page 61]
Internet-Draft             transactional-authz                 July 2020

   client ignores the longer interaction URL because both the long and
   short ones

   If the user scans the code, they are taken to the interaction
   endpoint and the AS looks up the current pending request based on the
   incoming URL.  If the user instead goes to the static page and enters
   the code manually, the AS looks up the current pending request based
   on the value of the user code.  In both cases, the user logs in, is
   identified as the RO for the resource being requested, and approves
   the request.  Once the request has been approved, the AS displays to
   the user a message to return to their device.

   Meanwhile, the client periodically polls the AS every 60 seconds at
   the continuation URL.

   POST /continue HTTP/1.1
   Host: server.example.com
   Content-type: application/json
   Detached-JWS: ejy0...

   {
       "handle": "80UPRY5NM33OMUKMKSKU"
   }

   The AS retrieves the pending request based on the handle and
   determines that it has not yet been authorized.  The AS indicates to
   the client that no access token has yet been issued but it can
   continue to call after another 60 second timeout.

   Content-type: application/json

   {
       "continue": {
           "handle": "BI9QNW6V9W3XFJK4R02D",
           "uri": "https://server.example.com/continue",
           "wait": 60
       }
   }

   Note that the continuation handle has been rotated since it was used
   by the client to make this call.  The client polls the continuation
   URL after a 60 second timeout using the new handle.

Richer                  Expires January 26, 2021               [Page 62]
Internet-Draft             transactional-authz                 July 2020

   POST /continue HTTP/1.1
   Host: server.example.com
   Content-type: application/json
   Detached-JWS: ejy0...

   {
       "handle": "BI9QNW6V9W3XFJK4R02D"
   }

   The AS retrieves the pending request based on the handle and
   determines that it has been approved and it issues an access token.

Content-type: application/json

{
    "access_token": {
        "value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
        "proof": "bearer",
        "manage": "https://server.example.com/token/PRY5NM33OM4TB8N6BW7OZB8CDFONP219RP1L",
        "resources": [
            "dolphin-metadata", "some other thing"
        ]
    }
}

C.3.  No User Involvement

   In this scenario, the client is requesting access on its own behalf,
   with no user to interact with.

   The client creates a request to the AS, identifying itself with its
   public key and using MTLS to make the request.

   POST /tx HTTP/1.1
   Host: server.example.com
   Content-type: application/json

   {
       "resources": [
           "backend service", "nightly-routine-3"
       ],
       "key": {
           "proof": "mtls",
           "cert#S256": "bwcK0esc3ACC3DB2Y5_lESsXE8o9ltc05O89jdN-dg2"
       }
   }

Richer                  Expires January 26, 2021               [Page 63]
Internet-Draft             transactional-authz                 July 2020

   The AS processes this and determines that the client can ask for the
   requested resources and issues an access token.

Content-type: application/json

{
    "access_token": {
        "value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
        "proof": "bearer",
        "manage": "https://server.example.com/token/PRY5NM33OM4TB8N6BW7OZB8CDFONP219RP1L",
        "resources": [
            "backend service", "nightly-routine-3"
        ]
    }
}

C.4.  Asynchronous Authorization

   In this scenario, the client is requesting on behalf of a specific
   RO, but has no way to interact with the user.  The AS can
   asynchronously reach out to the RO for approval in this scenario.

   The client starts the request at the AS by requesting a set of
   resources.  The client also identifies a particular user.

Richer                  Expires January 26, 2021               [Page 64]
Internet-Draft             transactional-authz                 July 2020

   POST /tx HTTP/1.1
   Host: server.example.com
   Content-type: application/json
   Detached-JWS: ejy0...

   {
       "resources": [
           {
               "type": "photo-api",
               "actions": [
                   "read",
                   "write",
                   "dolphin"
               ],
               "locations": [
                   "https://server.example.net/",
                   "https://resource.local/other"
               ],
               "datatypes": [
                   "metadata",
                   "images"
               ]
           },
           "read", "dolphin-metadata",
           {
               "type": "financial-transaction",
               "actions": [
                   "withdraw"
               ],
               "identifier": "account-14-32-32-3",
               "currency": "USD"
           },
           "some other thing"
       ],
       "key": "7C7C4AZ9KHRS6X63AJAO",
       "user": {
           "sub-ids": [ {
               "subject_type": "email",
               "email": "user@example.com"
           } ]
      }
   }

   The AS processes this and determines that the RO needs to interact.
   The AS determines that it can reach the identified user
   asynchronously and that the identified user does have the ability to
   approve this request.  The AS indicates to the client that it can
   poll for continuation.

Richer                  Expires January 26, 2021               [Page 65]
Internet-Draft             transactional-authz                 July 2020

   Content-type: application/json

   {
       "continue": {
           "handle": "80UPRY5NM33OMUKMKSKU",
           "uri": "https://server.example.com/continue",
           "wait": 60
       }
   }

   The AS reaches out to the RO and prompts them for consent.  In this
   example, the AS has an application that it can push notifications in
   to for the specified account.

   Meanwhile, the client periodically polls the AS every 60 seconds at
   the continuation URL.

   POST /continue HTTP/1.1
   Host: server.example.com
   Content-type: application/json
   Detached-JWS: ejy0...

   {
       "handle": "80UPRY5NM33OMUKMKSKU"
   }

   The AS retrieves the pending request based on the handle and
   determines that it has not yet been authorized.  The AS indicates to
   the client that no access token has yet been issued but it can
   continue to call after another 60 second timeout.

   Content-type: application/json

   {
       "continue": {
           "handle": "BI9QNW6V9W3XFJK4R02D",
           "uri": "https://server.example.com/continue",
           "wait": 60
       }
   }

   Note that the continuation handle has been rotated since it was used
   by the client to make this call.  The client polls the continuation
   URL after a 60 second timeout using the new handle.

Richer                  Expires January 26, 2021               [Page 66]
Internet-Draft             transactional-authz                 July 2020

   POST /continue HTTP/1.1
   Host: server.example.com
   Content-type: application/json
   Detached-JWS: ejy0...

   {
       "handle": "BI9QNW6V9W3XFJK4R02D"
   }

   The AS retrieves the pending request based on the handle and
   determines that it has been approved and it issues an access token.

Content-type: application/json

{
    "access_token": {
        "value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
        "proof": "bearer",
        "manage": "https://server.example.com/token/PRY5NM33OM4TB8N6BW7OZB8CDFONP219RP1L",
        "resources": [
            "dolphin-metadata", "some other thing"
        ]
    }
}

C.5.  Applying OAuth 2 Scopes and Client IDs

   In this scenario, the client developer has a client_id and set of
   scope values from their OAuth 2 system and wants to apply them to the
   new protocol.  Traditionally, the OAuth 2 client developer would put
   their client_id and scope values as parameters into a redirect
   request to the authorization endpoint.

   HTTP 302 Found
   Location: https://server.example.com/authorize
     ?client_id=7C7C4AZ9KHRS6X63AJAO
     &scope=read%20write%20dolphin
     &redirect_uri=https://client.example.net/return
     &response_type=code
     &state=123455

   Now the developer wants to make an analogous request to the AS using
   the new protocol.  To do so, the client makes an HTTP POST and places
   the OAuth 2 values in the appropriate places.

Richer                  Expires January 26, 2021               [Page 67]
Internet-Draft             transactional-authz                 July 2020

   POST /tx HTTP/1.1
   Host: server.example.com
   Content-type: application/json
   Detached-JWS: ejy0...

   {
       "resources": [
           "read", "write", "dolphin"
       ],
       "key": "7C7C4AZ9KHRS6X63AJAO",
       "interact": {
           "redirect": true,
           "callback": {
               "uri": "https://client.example.net/return?state=123455",
               "nonce": "LKLTI25DK82FX4T4QFZC"
           }
       }
   }

   The client_id can be used to identify the client's keys that it uses
   for authentication, the scopes represent resources that the client is
   requesting, and the redirect_uri and state value are combined into a
   callback URI that can be unique per request.  The client additionally
   creates a nonce to protect the callback, separate from the state
   parameter that it has added to its return URL.

   From here, the protocol continues as above.

Author's Address

   Justin Richer (editor)
   Bespoke Engineering

   Email: ietf@justin.richer.org

Richer                  Expires January 26, 2021               [Page 68]