The OAuth 2.0 Authorization Framework: JWT Pop Token Usage
draft-sakimura-oauth-jpop-00

OAuth Working Group                                          N. Sakimura
Internet-Draft                                 Nomura Research Institute
Intended status: Standards Track                                   K. Li
Expires: September 11, 2017                                Alibaba Group
                                                              J. Bradley
                                                           Ping Identity
                                                          March 10, 2017

       The OAuth 2.0 Authorization Framework: JWT Pop Token Usage
                      draft-sakimura-oauth-jpop-00

Abstract

   This specification describes how to use JWT POP (Jpop) tokens that
   were obtained through [POPKD] in HTTP requests to access OAuth 2.0
   protected resources.  Only the party in possession of a corresponding
   cryptographic key with the Jpop token can use it to get access to the
   associated resources unlike in the case of the bearer token described
   in [RFC6750] where any party in posession of the access token can
   access the resource.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

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
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   This Internet-Draft will expire on September 11, 2017.

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Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . .   3
   2.  Terms and definitions . . . . . . . . . . . . . . . . . . . .   3
   3.  JWT POP Token . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Sender Constrained Token  . . . . . . . . . . . . . . . . . .   4
     4.1.  CN Constrained Token  . . . . . . . . . . . . . . . . . .   4
     4.2.  Client ID Constrained Token . . . . . . . . . . . . . . .   4
   5.  Key Constrained Token . . . . . . . . . . . . . . . . . . . .   5
   6.  Resource access method  . . . . . . . . . . . . . . . . . . .   5
     6.1.  CN method . . . . . . . . . . . . . . . . . . . . . . . .   6
     6.2.  Signature method  . . . . . . . . . . . . . . . . . . . .   6
   7.  Authorization Error . . . . . . . . . . . . . . . . . . . . .   7
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
     8.1.  Jpop Authentication Scheme  . . . . . . . . . . . . . . .   7
     8.2.  JWT Confirmation Methods  . . . . . . . . . . . . . . . .   8
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
     9.1.  Certificate validation  . . . . . . . . . . . . . . . . .   8
     9.2.  Key protection  . . . . . . . . . . . . . . . . . . . . .   8
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     11.1.  Normative References . . . . . . . . . . . . . . . . . .   9
     11.2.  Informative References . . . . . . . . . . . . . . . . .  10
   Appendix A.  Document History . . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   This document specifies the method for the client to use a proof-of-
   possestion token against a protected resource.  The format of such
   token is defined in section 3 of [RFC7800].

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1.1.  Notational Conventions

   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 RFC
   2119 [RFC2119].

   Unless otherwise noted, all the protocol parameter names and values
   are case sensitive.

2.  Terms and definitions

   For the purpose of this document, the terms defined in [RFC6749] and
   [RFC7800] are used.

3.  JWT POP Token

   JWT PoP token is a JWS signed JWT whose payload is a JWT Claims Set.
   The JWT claims set MUST include the following:

   iss  The issuer identifier of the auhtorization server.

   aud  The identifier of the resource server.

   iat  The issuance time of this token.

   exp  The expiry time of this token.

   cnf  The confirmation method.

   Their semantics are defined in [RFC7519] and [RFC7800].

   Following is an example of such.

        {
         "iss": "https://server.example.com",
         "aud": "https://resource.example.org",
         "iat": "1360189224",
         "exp": "1361398868",
         "cnf":{...}
        }

                    Figure 1: Example of JWT PoP Token.

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4.  Sender Constrained Token

   There are several varieties of sender constrained token.  Namely:

   1.  CN Constrained Token

   2.  Client ID Constrained Token

4.1.  CN Constrained Token

   CN constrained token is typically used when X.509 client certificate
   authentication is used at the token endpoint.  In this case, the
   constraint is expressed by including the following member at the top
   level of cnf claim.

   cn The Common Name of the client certificate that the client used in
      the authorization request.

   The authorization server finds the relevant CN from the X.509 client
   certificate authentication that is performed at the token endpoint.

   {
   "iss": "https://server.example.com",
   "sub": "joe@example.com",
   "aud": "https://resource.example.org",
   "exp": "1361398824",
   "nbf": "1360189224",
   "cnf":{
     "cn": "client.example.com"
   }

                 Figure 2: Example of CN Constrained JWT.

4.2.  Client ID Constrained Token

   The constraint in the Client ID constrained token is expressed by
   including the following member at the top level of cnf claim.

   cid  The client_id of the client that the client used in the
      authorization request.  The combination of the "iss" of the access
      token and this value forms a globally unique identifier for the
      client.

   The authorization server finds the client ID from the client ID used
   in the client authentication at the token endpoint.

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5.  Key Constrained Token

   Methods to express key constraints are extensively described in the
   section 3 of [RFC7800].  Such cnf claim is used in the access token
   described in section 3 to form a key constrained token.  [RFC7800]
   defines 4 confirmation methods.

   jwk  JSON Web Key Representing Public Key

   jwe  Encrypted JSON Web Key

   kid  Key Identifier

   jku  JWK Set URL

   Following is an example of such JWT payload.

        {
         "iss": "https://server.example.com",
         "sub": "joe@example.com",
         "aud": "https://resource.example.org",
         "exp": "1361398824",
         "nbf": "1360189224",
         "cnf":{
           "jwk":{
             "kty": "EC",
             "use": "sig",
             "crv": "P-256",
             "x": "18wHLeIgW9wVN6VD1Txgpqy2LszYkMf6J8njVAibvhM",
             "y": "-V4dS4UaLMgP_4fY4j8ir7cl1TXlFdAgcx55o7TkcSA"
            }
          }
        }

                Figure 3: Example of a Key Constrained JWT.

6.  Resource access method

   The resource server that supports this specification MUST
   authenticate the Client by having it demonstrate that it is the
   holder of the key associated with the access token being used.  The
   confirmation method can be broadly categorized in two forms.

   CN method  A method leveraging on the X.509 client certificate
      authentication

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   Signature method  A method leveraging the signature on the nonce.
      Cases with confirmation methods equal to one of cid, jwk, jwe,
      kid, and jku falls into this category.

6.1.  CN method

   Under this method, X.509 client certificate authentication at the
   resource endpoint is being leveraged.  The resource endpoint MUST
   obtain the CN of the client certificate used for the authentication
   and MUST verify that the value of the cn member in the cnf member
   matches with it.

   If it does not match, the process stops here and the resource access
   MUST be denied.

   If it was valid, then the resource server MUST verify the access
   token.  If it is valid, the resource SHOULD be returned as HTTP
   response.

6.2.  Signature method

   For this, the following steps are taken:

   1.  The client prepares a nonce.

   2.  The client creates JWS compact serialization over the nonce.

   To obtain it, first create a JSON with a name "nonce" and the value
   being what was received in the previous step. e.g.,

   {
           "nonce":"dcd98b7102dd2f0e8b11d0f600bfb0c093"
   }

   Then, "jws-on-nonce" is obtained by creating a compact serialization
   of JWS on this JSON.

   3.  The client sends the request to the resource server, this time
   with Authorization Request Header as defined in section 4.2 of
   [RFC7235] with the credential as follows:

        credentials      =  "Jpop" jpop-response
        jpop-response    =  at-response "," s-response
        at-response      =  "at" "=" access-token; As specified by [POPKD]
        s-response       =  "s" "=" jws-on-nonce; Created in the step 3.
        access-token     =  quoted-string
        jws-on-nonce     =  quoted-string

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   In the following example, the access token and the jws-on-nonce are
   represented as access.token.jwt and jws.of.nonce for the sake of
   brevity.

           GET /resource/1234 HTTP/1.0
           Host: server.example.com
           Authorization: Jpop at="access.token.jwt", s="jws.of.nonce"

                     Figure 4: Example resouce request

   4.  The resource server finds the client's public key form the access
   token through the methods described in [RFC7800].

   5.  The resource server MUST verify the value of "s" of the
   Authorization header.  If it fails, the process stops here and the
   resource access MUST be denied.

   6.  The resource server MUST verify the access token.  If it is
   valid, the resource SHOULD be returned as HTTP response.

7.  Authorization Error

   If the client requests the resource without the proper authoization
   header, the resource server returns a HTTP 401 response with "WWW-
   Authenticate" header as defined in section 4.1 of [RFC7235] with the
   challenge as follows:

             challenge        =  "Jpop" jpop-challenge
             jpop-challenge   =  "nonce" "=" nonce-value
             nonce-value      =  quoted-string

   Following example depicts what the response would look like.

   HTTP/1.0 401 Unauthorized
   Server: HTTPd/0.9
   Date: Wed, 14 March 2017 09:26:53 GMT
   WWW-Authenticate: Jpop nonce="dcd98b7102dd2f0e8b11d0f600bfb0c093"

                     Figure 5: Example error response.

8.  IANA Considerations

8.1.  Jpop Authentication Scheme

   A new scheme has been registered in the HTTP Authentication Scheme
   Registry as follows:

   Authentication Scheme Name: Jpop

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   Reference: Section 3 of this specification

   Notes (optional): The Named Authentication scheme is intended to be
   used only with OAuth Resource Access, and thus does not support proxy
   authentication.

8.2.  JWT Confirmation Methods

   o  Confirmation Method Value: "cn"

   o  Confirmation Method Description: CN match with the TLS client
      auth.

   o  Change Controller: IESG

   o  Specification Document(s): This document.

   o  Confirmation Method Value: "cid"

   o  Confirmation Method Description: Client ID Confirmation

   o  Change Controller: IESG

   o  Specification Document(s): This document.

9.  Security Considerations

9.1.  Certificate validation

   The "cn" JWT confirmation method relies its security property on the
   X.509 client certificate authentication.  In particular, the validity
   of the certificate needs to be verified properly.  It involves the
   traversal of all the certificate chain and the certificate validation
   (e.g., with OCSP).

9.2.  Key protection

   The client's secret key must be kept securely.  Otherwise, the notion
   of PoP breaks down.

   It should be noted that JWE confirmation method is significantly
   weaker form of the PoP, as the resource server and the authorization
   server can masquerade as the client.

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10.  Acknowledgements

   The authors thank the following people for providing valuable
   feedback to this document.  Nov Matake (YAuth).

11.  References

11.1.  Normative References

   [POPKD]    Bradley, J., Hunt, P., Jones, M., and H. Tschofenig,
              "OAuth 2.0 Proof-of-Possession: Authorization Server to
              Client Key Distribution", March 2017,
              <https://tools.ietf.org/html/draft-ietf-oauth-pop-key-
              distribution-03>.

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

   [RFC2617]  Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
              Leach, P., Luotonen, A., and L. Stewart, "HTTP
              Authentication: Basic and Digest Access Authentication",
              RFC 2617, DOI 10.17487/RFC2617, June 1999,
              <http://www.rfc-editor.org/info/rfc2617>.

   [RFC6749]  Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
              RFC 6749, DOI 10.17487/RFC6749, October 2012,
              <http://www.rfc-editor.org/info/rfc6749>.

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

   [RFC7235]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Authentication", RFC 7235,
              DOI 10.17487/RFC7235, June 2014,
              <http://www.rfc-editor.org/info/rfc7235>.

   [RFC7519]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
              (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
              <http://www.rfc-editor.org/info/rfc7519>.

   [RFC7800]  Jones, M., Bradley, J., and H. Tschofenig, "Proof-of-
              Possession Key Semantics for JSON Web Tokens (JWTs)",
              RFC 7800, DOI 10.17487/RFC7800, April 2016,
              <http://www.rfc-editor.org/info/rfc7800>.

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11.2.  Informative References

   [PKCE]     Sakimura, N., "Proof Key for Code Exchange by OAuth Public
              Clients", July 2015.

   [POPA]     Hunt, P., Ed., "OAuth 2.0 Proof-of-Possession (PoP)
              Security Architecture", March 2015,
              <https://tools.ietf.org/html/draft-ietf-oauth-pop-
              architecture-08>.

   [TINTRO]   Richer, J., "OAuth 2.0 Token Introspection", July 2015.

Appendix A.  Document History

   -00  Initial Version.

Authors' Addresses

   Nat Sakimura
   Nomura Research Institute
   Otemachi Financial City Grand Cube, 1-9-2 Otemachi
   Chiyoda-ku, Tokyo  100-0004
   Japan

   Phone: +81-3-5533-2111
   Email: n-sakimura@nri.co.jp
   URI:   https://nat.sakimura.org/

   Kepeng Li
   Alibaba Group

   Email: kepeng.lkp@alibaba-inc.com

   John Bradley
   Ping Identity

   Email: ve7jtb@ve7jtb.com
   URI:   http://www.thread-safe.com/

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