Push-Based Security Event Token (SET) Delivery Using HTTP
draft-ietf-secevent-http-push-14

Document Type Active Internet-Draft (secevent WG)
Last updated 2020-07-02 (latest revision 2020-06-26)
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Security Events Working Group                            A. Backman, Ed.
Internet-Draft                                                    Amazon
Intended status: Standards Track                           M. Jones, Ed.
Expires: December 28, 2020                                     Microsoft
                                                            M. Scurtescu
                                                                Coinbase
                                                               M. Ansari
                                                                   Cisco
                                                              A. Nadalin
                                                               Microsoft
                                                           June 26, 2020

       Push-Based Security Event Token (SET) Delivery Using HTTP
                    draft-ietf-secevent-http-push-14

Abstract

   This specification defines how a Security Event Token (SET) can be
   delivered to an intended recipient using HTTP POST over TLS.  The SET
   is transmitted in the body of an HTTP POST request to an endpoint
   operated by the recipient, and the recipient indicates successful or
   failed transmission via the HTTP response.

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 December 28, 2020.

Copyright Notice

   Copyright (c) 2020 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
   Provisions Relating to IETF Documents

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   (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.  Introduction and Overview . . . . . . . . . . . . . . . . . .   2
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . .   3
     1.2.  Definitions . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  SET Delivery  . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Transmitting a SET  . . . . . . . . . . . . . . . . . . .   5
     2.2.  Success Response  . . . . . . . . . . . . . . . . . . . .   6
     2.3.  Failure Response  . . . . . . . . . . . . . . . . . . . .   6
     2.4.  Security Event Token Delivery Error Codes . . . . . . . .   8
   3.  Authentication and Authorization  . . . . . . . . . . . . . .   9
   4.  Delivery Reliability  . . . . . . . . . . . . . . . . . . . .   9
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
     5.1.  Authentication Using Signed SETs  . . . . . . . . . . . .  10
     5.2.  HTTP Considerations . . . . . . . . . . . . . . . . . . .  10
     5.3.  Confidentiality of SETs . . . . . . . . . . . . . . . . .  10
     5.4.  Denial of Service . . . . . . . . . . . . . . . . . . . .  11
     5.5.  Authenticating Persisted SETs . . . . . . . . . . . . . .  11
   6.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  11
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
     7.1.  Security Event Token Delivery Error Codes . . . . . . . .  12
       7.1.1.  Registration Template . . . . . . . . . . . . . . . .  13
       7.1.2.  Initial Registry Contents . . . . . . . . . . . . . .  13
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  14
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  16
   Appendix A.  Unencrypted Transport Considerations . . . . . . . .  16
   Appendix B.  Other Streaming Specifications . . . . . . . . . . .  17
   Appendix C.  Acknowledgments  . . . . . . . . . . . . . . . . . .  18
   Appendix D.  Change Log . . . . . . . . . . . . . . . . . . . . .  19
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  24

1.  Introduction and Overview

   This specification defines a mechanism by which a transmitter of a
   Security Event Token (SET) [RFC8417] can deliver the SET to an
   intended SET Recipient via HTTP POST [RFC7231] over TLS.  This is an
   alternative SET delivery method to the one defined in
   [I-D.ietf-secevent-http-poll].

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   Push-based SET delivery over HTTP POST is intended for scenarios
   where all of the following apply:

   o  The transmitter of the SET is capable of making outbound HTTP
      requests.

   o  The recipient is capable of hosting a TLS-enabled HTTP endpoint
      that is accessible to the transmitter.

   o  The transmitter and recipient are willing to exchange data with
      one another.

   In some scenarios, either push-based or poll-based delivery could be
   used, and in others, only one of them would be applicable.

   A mechanism for exchanging configuration metadata such as endpoint
   URLs, cryptographic keys, and possible implementation constraints
   such as buffer size limitations between the transmitter and recipient
   is out of scope for this specification.  How SETs are defined and the
   process by which security events are identified for SET Recipients
   are specified in [RFC8417].

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 BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   Throughout this document, all figures may contain spaces and extra
   line wrapping for readability and due to space limitations.

1.2.  Definitions

   This specification utilizes the following terms defined in [RFC8417]:
   "Security Event Token (SET)", "SET Issuer", "SET Recipient", and
   "Event Payload", as well as the term defined below:

   SET Transmitter  An entity that delivers SETs in its possession to
      one or more SET Recipients.

2.  SET Delivery

   To deliver a SET to a given SET Recipient, the SET Transmitter makes
   a SET transmission request to the SET Recipient, with the SET itself
   contained within the request.  The SET Recipient replies to this
   request with a response either acknowledging successful transmission

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   of the SET or indicating that an error occurred while receiving,
   parsing, and/or validating the SET.

   Upon receipt of a SET, the SET Recipient SHALL validate that all of
   the following are true:

   o  The SET Recipient can parse the SET.

   o  The SET is authentic (i.e., it was issued by the issuer specified
      within the SET, and if signed, was signed by a key belonging to
      the issuer).

   o  The SET Recipient is identified as an intended audience of the
      SET.

   o  The SET Issuer is recognized as an issuer that the SET Recipient
      is willing to receive SETs from (e.g., the issuer is listed as
      allowed by the SET Recipient).

   o  The SET Recipient is willing to accept this SET from this SET
      Transmitter (e.g., the SET Transmitter is expected to send SETs
      with the issuer and subject of the SET in question).

   The mechanisms by which the SET Recipient performs this validation
   are out of scope for this document.  SET parsing, issuer
   identification, and audience identification are defined in [RFC8417].
   The mechanism for validating the authenticity of a SET is deployment
   specific, and may vary depending on the authentication mechanisms in
   use, and whether the SET is signed and/or encrypted (See Section 3).

   SET Transmitters MAY transmit SETs issued by another entity.  The SET
   Recipient may accept or reject (i.e., return an error response such
   as "access_denied") a SET at its own discretion.

   The SET Recipient persists the SET in a way that is sufficient to
   meet the SET Recipient's own reliability requirements.  The level and
   method of retention of SETs by SET Recipients is out of scope of this
   specification.  Once the SET has been validated and persisted, the
   SET Recipient SHOULD immediately return a response indicating that
   the SET was successfully delivered.  The SET Recipient SHOULD NOT
   perform further processing of the SET beyond the required validation
   steps prior to sending this response.  Any additional steps SHOULD be
   executed asynchronously from delivery to minimize the time the SET
   Transmitter is waiting for a response.

   The SET Transmitter MAY transmit the same SET to the SET Recipient
   multiple times, regardless of the response from the SET Recipient.
   The SET Recipient MUST respond as it would if the SET had not been

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   previously received by the SET Recipient.  The SET Recipient MUST NOT
   expect or depend on a SET Transmitter to re-transmit a SET or
   otherwise make a SET available to the SET Recipient once the SET
   Recipient acknowledges that it was received successfully.

   The SET Transmitter should not re-transmit a SET unless the SET
   Transmitter suspects that previous transmissions may have failed due
   to potentially recoverable errors (such as network outage or
   temporary service interruption at either the SET Transmitter or SET
   Recipient).  In all other cases, the SET Transmitter SHOULD NOT re-
   transmit a SET.  The SET Transmitter SHOULD delay retransmission for
   an appropriate amount of time to avoid overwhelming the SET Recipient
   (see Section 4).

2.1.  Transmitting a SET

   To transmit a SET to a SET Recipient, the SET Transmitter makes an
   HTTP POST request to a TLS-enabled HTTP endpoint provided by the SET
   Recipient.  The "Content-Type" header field of this request MUST be
   "application/secevent+jwt" as defined in Sections 2.3 and 7.2 of
   [RFC8417], and the "Accept" header field MUST be "application/json".
   The request body MUST consist of the SET itself, represented as a JWT
   [RFC7519].

   The SET Transmitter MAY include in the request an "Accept-Language"
   header field to indicate to the SET Recipient the preferred
   language(s) in which to receive error messages.

   The mechanisms by which the SET Transmitter determines the HTTP
   endpoint to use when transmitting a SET to a given SET Recipient are
   not defined by this specification and are deployment specific.

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   The following is a non-normative example of a SET transmission
   request:

     POST /Events HTTP/1.1
     Host: notify.rp.example.com
     Accept: application/json
     Accept-Language: en-US, en;q=0.5
     Content-Type: application/secevent+jwt

     eyJ0eXAiOiJzZWNldmVudCtqd3QiLCJhbGciOiJIUzI1NiJ9Cg
     .
     eyJpc3MiOiJodHRwczovL2lkcC5leGFtcGxlLmNvbS8iLCJqdGkiOiI3NTZFNjk
     3MTc1NjUyMDY5NjQ2NTZFNzQ2OTY2Njk2NTcyIiwiaWF0IjoxNTA4MTg0ODQ1LC
     JhdWQiOiI2MzZDNjk2NTZFNzQ1RjY5NjQiLCJldmVudHMiOnsiaHR0cHM6Ly9zY
     2hlbWFzLm9wZW5pZC5uZXQvc2VjZXZlbnQvcmlzYy9ldmVudC10eXBlL2FjY291
     bnQtZGlzYWJsZWQiOnsic3ViamVjdCI6eyJzdWJqZWN0X3R5cGUiOiJpc3Mtc3V
     iIiwiaXNzIjoiaHR0cHM6Ly9pZHAuZXhhbXBsZS5jb20vIiwic3ViIjoiNzM3NT
     YyNkE2NTYzNzQifSwicmVhc29uIjoiaGlqYWNraW5nIn19fQ
     .
     Y4rXxMD406P2edv00cr9Wf3_XwNtLjB9n-jTqN1_lLc

                Figure 1: Example SET Transmission Request

2.2.  Success Response

   If the SET is determined to be valid, the SET Recipient SHALL
   acknowledge successful transmission by responding with HTTP Response
   Status Code 202 (Accepted) (see Section 6.3.3 of [RFC7231]).  The
   body of the response MUST be empty.

   The following is a non-normative example of a successful receipt of a
   SET.

     HTTP/1.1 202 Accepted

              Figure 2: Example Successful Delivery Response

2.3.  Failure Response

   In the event of a general HTTP error condition, the SET Recipient
   responds with the applicable HTTP Status Code, as defined in
   Section 6 of [RFC7231].

   When the SET Recipient detects an error parsing, validating, or
   authenticating a SET transmitted in a SET Transmission Request, the
   SET Recipient SHALL respond with an HTTP Response Status Code of 400
   (Bad Request).  The "Content-Type" header field of this response MUST

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   be "application/json", and the body MUST be a UTF-8 encoded JSON
   [RFC8259] object containing the following name/value pairs:

   err  A Security Event Token Error Code (see Section 2.4).

   description  A UTF-8 string containing a human-readable description
      of the error that may provide additional diagnostic information.
      The exact content of this field is implementation specific.

   The response MUST include a "Content-Language" header field, whose
   value indicates the language of the error descriptions included in
   the response body.  If the SET Recipient can provide error
   descriptions in multiple languages, they SHOULD choose the language
   to use according to the value of the "Accept-Language" header field
   sent by the SET Transmitter in the transmission request, as described
   in Section 5.3.5 of [RFC7231].  If the SET Transmitter did not send
   an "Accept-Language" header field, or if the SET Recipient does not
   support any of the languages included in the header field, the SET
   Recipient MUST respond with messages that are understandable by an
   English-speaking person, as described in Section 4.5 of [RFC2277].

   The following is a non-normative example error response indicating
   that the key used to encrypt the SET has been revoked.

     HTTP/1.1 400 Bad Request
     Content-Language: en-US
     Content-Type: application/json

     {
       "err": "invalid_key",
       "description": "Key ID 12345 has been revoked."
     }

              Figure 3: Example Error Response (invalid_key)

   The following is a non-normative example error response indicating
   that the access token included in the request is expired.

     HTTP/1.1 400 Bad Request
     Content-Language: en-US
     Content-Type: application/json

     {
       "err": "authentication_failed",
       "description": "Access token has expired."
     }

         Figure 4: Example Error Response (authentication_failed)

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   The following is a non-normative example error response indicating
   that the SET Receiver is not willing to accept SETs issued by the
   specified issuer from this particular SET Transmitter.

  HTTP/1.1 400 Bad Request
  Content-Language: en-US
  Content-Type: application/json

  {
    "err": "invalid_issuer",
    "description": "Not authorized for issuer https://iss.example.com/."
  }

             Figure 5: Example Error Response (access_denied)

2.4.  Security Event Token Delivery Error Codes

   Security Event Token Delivery Error Codes are strings that identify a
   specific category of error that may occur when parsing or validating
   a SET.  Every Security Event Token Delivery Error Code MUST have a
   unique name registered in the IANA "Security Event Token Delivery
   Error Codes" registry established by Section 7.1.

   The following table presents the initial set of Error Codes that are
   registered in the IANA "Security Event Token Delivery Error Codes"
   registry:

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   +-----------------------+-------------------------------------------+
   | Error Code            | Description                               |
   +-----------------------+-------------------------------------------+
   | invalid_request       | The request body cannot be parsed as a    |
   |                       | SET, or the Event Payload within the SET  |
   |                       | does not conform to the event's           |
   |                       | definition.                               |
   | invalid_key           | One or more keys used to encrypt or sign  |
   |                       | the SET is invalid or otherwise           |
   |                       | unacceptable to the SET Recipient         |
   |                       | (expired, revoked, failed certificate     |
   |                       | validation, etc.).                        |
   | invalid_issuer        | The SET issuer is invalid for the SET     |
   |                       | Recipient.                                |
   | invalid_audience      | The SET audience does not correspond to   |
   |                       | the SET Recipient.                        |
   | authentication_failed | The SET Recipient could not authenticate  |
   |                       | the SET Transmitter.                      |
   | access_denied         | The SET Transmitter is not authorized to  |
   |                       | transmit the SET to the SET Recipient.    |
   +-----------------------+-------------------------------------------+

                     Table 1: SET Delivery Error Codes

   Other Error Codes may also be received, as the set of Error Codes is
   extensible via the IANA "Security Event Token Delivery Error Codes"
   registry established in Section 7.1.

3.  Authentication and Authorization

   The SET delivery method described in this specification is based upon
   HTTP over TLS [RFC2818] and standard HTTP authentication and
   authorization schemes, as per [RFC7235].  The TLS server certificate
   MUST be validated using DNS-ID [RFC6125] and/or DANE [RFC6698].

   Authorization for the eligibility to provide actionable SETs can be
   determined by using the identity of the SET Issuer, the identity of
   the SET Transmitter, perhaps using mutual TLS, or via other employed
   authentication methods.  Because SETs are not commands, SET
   Recipients are free to ignore SETs that are not of interest.

4.  Delivery Reliability

   Delivery reliability requirements may vary depending upon the use
   cases.  This specification defines the response from the SET
   Recipient in such a way as to provide the SET Transmitter with the
   information necessary to determine what further action is required,
   if any, in order to meet their requirements.  SET Transmitters with

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   high reliability requirements may be tempted to always retry failed
   transmissions.  However, it should be noted that for many types of
   SET delivery errors, a retry is extremely unlikely to be successful.
   For example, "invalid_request" indicates a structural error in the
   content of the request body that is likely to remain when re-
   transmitting the same SET.  Others such as "access_denied" may be
   transient, for example if the SET Transmitter refreshes expired
   credentials prior to re-transmission.

   The SET Transmitter may be unaware of whether or not a SET has been
   delivered to a SET Recipient.  For example, a network interruption
   could prevent the SET Transmitter from receiving the success
   response, or a service outage could prevent the SET Transmitter from
   recording the fact that the SET was delivered.  It is left to the
   implementer to decide how to handle such cases, based on their
   requirements.  For example, it may be appropriate for the SET
   Transmitter to re-transmit the SET to the SET Recipient, erring on
   the side of guaranteeing delivery, or it may be appropriate to assume
   delivery was successful, erring on the side of not spending resources
   re-transmitting previously delivered SETs.  Other options, such as
   sending the SET to a "dead letter queue" for manual examination may
   also be appropriate.

   Implementers SHOULD evaluate the reliability requirements of their
   use cases and the impact of various retry mechanisms and re-
   transmission policies on the performance of their systems to
   determine an appropriate strategy for handling various error
   conditions.

5.  Security Considerations

5.1.  Authentication Using Signed SETs

   JWS signed SETs can be used (see [RFC7515] and Section 5 of
   [RFC8417]) to enable the SET Recipient to validate that the SET
   Issuer is authorized to provide actionable SETs.

5.2.  HTTP Considerations

   SET delivery depends on the use of Hypertext Transfer Protocol and is
   thus subject to the security considerations of HTTP Section 9 of
   [RFC7230] and its related specifications.

5.3.  Confidentiality of SETs

   SETs may contain sensitive information, including Personally
   Identifiable Information (PII), or be distributed through third
   parties.  In such cases, SET Transmitters and SET Recipients MUST

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   protect the confidentiality of the SET contents.  TLS MUST be used to
   secure the transmitted SETs.  In some use cases, encrypting the SET
   as described in JWE [RFC7516] will also be required.  The Event
   delivery endpoint MUST support at least TLS version 1.2 [RFC5246] and
   SHOULD support the newest version of TLS that meets its security
   requirements, which as of the time of this publication is TLS 1.3
   [RFC8446].  The client MUST perform a TLS/SSL server certificate
   check using DNS-ID [RFC6125] and/or DANE [RFC6698].  How a SET
   Transmitter determines the expected service identity to match the SET
   Recipient's server certificate against is out of scope for this
   document.  The implementation security considerations for TLS in
   "Recommendations for Secure Use of TLS and DTLS" [RFC7525] MUST be
   followed.

5.4.  Denial of Service

   The SET Recipient may be vulnerable to a denial-of-service attack
   where a malicious party makes a high volume of requests containing
   invalid SETs, causing the endpoint to expend significant resources on
   cryptographic operations that are bound to fail.  This may be
   mitigated by authenticating SET Transmitters with a mechanism such as
   mutual TLS.  Rate-limiting problematic transmitters is also a
   possible means of mitigation.

5.5.  Authenticating Persisted SETs

   At the time of receipt, the SET Recipient can rely upon TLS
   mechanisms, HTTP authentication methods, and/or other context from
   the transmission request to authenticate the SET Transmitter and
   validate the authenticity of the SET.  However, this context is
   typically unavailable to systems to which the SET Recipient forwards
   the SET, or to systems that retrieve the SET from storage.  If the
   SET Recipient requires the ability to validate SET authenticity
   outside of the context of the transmission request, then the SET
   Recipient SHOULD ensure that such SETs have been signed in accordance
   with [RFC7515].  Needed context could also be stored with the SET and
   retrieved with it.

6.  Privacy Considerations

   SET Transmitters should attempt to deliver SETs that are targeted to
   the specific business and protocol needs of subscribers.

   When sharing personally identifiable information or information that
   is otherwise considered confidential to affected users, SET
   Transmitters and Recipients MUST have the appropriate legal
   agreements and user consent or terms of service in place.
   Furthermore, data that needs confidentiality protection MUST be

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   encrypted, at least with TLS and sometimes also using JSON Web
   Encryption (JWE) [RFC7516].

   In some cases, subject identifiers themselves may be considered
   sensitive information, such that their inclusion within a SET may be
   considered a violation of privacy.  SET Issuers and SET Transmitters
   should consider the ramifications of sharing a particular subject
   identifier with a SET Recipient (e.g., whether doing so could enable
   correlation and/or de-anonymization of data) and choose appropriate
   subject identifiers for their use cases.

7.  IANA Considerations

7.1.  Security Event Token Delivery Error Codes

   This document defines Security Event Token Delivery Error Codes, for
   which IANA is asked to create and maintain a new registry titled
   "Security Event Token Delivery Error Codes".  Initial values for the
   Security Event Token Delivery Error Codes registry are defined in
   Table 1 and registered below.  Future assignments are to be made
   through the Specification Required registration policy ([RFC8126])
   and shall follow the template below.

   Error Codes are intended to be interpreted by automated systems, and
   therefore SHOULD identify classes of errors to which an automated
   system could respond in a meaningfully distinct way (e.g., by
   refreshing authentication credentials and retrying the request).

   Error Code names are case sensitive.  Names may not match other
   registered names in a case-insensitive manner unless the Designated
   Experts state that there is a compelling reason to allow an
   exception.

   Criteria that should be applied by the Designated Experts includes
   determining whether the proposed registration duplicates existing
   functionality, whether it is likely to be of general applicability or
   whether it is useful only for a single application, and whether the
   registration description is clear.

   It is suggested that multiple Designated Experts be appointed who are
   able to represent the perspectives of different applications using
   this specification, in order to enable broadly informed review of
   registration decisions.  In cases where a registration decision could
   be perceived as creating a conflict of interest for a particular
   Expert, that Expert should defer to the judgment of the other
   Experts.

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7.1.1.  Registration Template

   Error Code
      The name of the Security Event Token Delivery Error Code, as
      described in Section 2.4.  The name MUST be a case-sensitive ASCII
      string consisting only of letters, digits, and underscore; these
      are the characters whose codes fall within the inclusive ranges
      0x30-39, 0x41-5A, 0x5F and 0x61-7A.

   Description
      A brief human-readable description of the Security Event Token
      Delivery Error Code.

   Change Controller
      For error codes registered by the IETF or its working groups, list
      "IETF".  For all other error codes, list the name of the party
      responsible for the registration.  Contact information such as
      mailing address, email address, or phone number may also be
      provided.

   Defining Document(s)
      A reference to the document or documents that define the Security
      Event Token Delivery Error Code.  The definition MUST specify the
      name and description of the error code and explain under what
      circumstances the error code may be used.  URIs that can be used
      to retrieve copies of each document at no cost SHOULD be included.

7.1.2.  Initial Registry Contents

      Error Code: invalid_request
      Description: The request body cannot be parsed as a SET or the
      event payload within the SET does not conform to the event's
      definition.
      Change Controller: IETF
      Defining Document(s): Section 2.4 of [[ this specification ]]

      Error Code: invalid_key
      Description: One or more keys used to encrypt or sign the SET is
      invalid or otherwise unacceptable to the SET Recipient (expired,
      revoked, failed certificate validation, etc.).
      Change Controller: IETF
      Defining Document(s): Section 2.4 of [[ this specification ]]

      Error Code: invalid_issuer
      Description: The SET issuer is invalid for the SET Recipient.
      Change Controller: IETF
      Defining Document(s): Section 2.4 of [[ this specification ]]

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      Error Code: invalid_audience
      Description: The SET audience does not correspond to the SET
      Recipient.
      Change Controller: IETF
      Defining Document(s): Section 2.4 of [[ this specification ]]

      Error Code: authentication_failed
      Description: The SET Recipient could not authenticate the SET
      Transmitter.
      Change Controller: IETF
      Defining Document(s): Section 2.4 of [[ this specification ]]

      Error Code: access_denied
      Description: The SET Transmitter is not authorized to transmit the
      SET to the SET Recipient.
      Change Controller: IETF
      Defining Document(s): Section 2.4 of [[ this specification ]]

8.  References

8.1.  Normative References

   [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>.

   [RFC2277]  Alvestrand, H., "IETF Policy on Character Sets and
              Languages", BCP 18, RFC 2277, DOI 10.17487/RFC2277,
              January 1998, <https://www.rfc-editor.org/info/rfc2277>.

   [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818,
              DOI 10.17487/RFC2818, May 2000,
              <https://www.rfc-editor.org/info/rfc2818>.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <https://www.rfc-editor.org/info/rfc5246>.

   [RFC6125]  Saint-Andre, P. and J. Hodges, "Representation and
              Verification of Domain-Based Application Service Identity
              within Internet Public Key Infrastructure Using X.509
              (PKIX) Certificates in the Context of Transport Layer
              Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
              2011, <https://www.rfc-editor.org/info/rfc6125>.

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   [RFC6698]  Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
              of Named Entities (DANE) Transport Layer Security (TLS)
              Protocol: TLSA", RFC 6698, DOI 10.17487/RFC6698, August
              2012, <https://www.rfc-editor.org/info/rfc6698>.

   [RFC7230]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Message Syntax and Routing",
              RFC 7230, DOI 10.17487/RFC7230, June 2014,
              <https://www.rfc-editor.org/info/rfc7230>.

   [RFC7231]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
              DOI 10.17487/RFC7231, June 2014,
              <https://www.rfc-editor.org/info/rfc7231>.

   [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>.

   [RFC7516]  Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)",
              RFC 7516, DOI 10.17487/RFC7516, May 2015,
              <https://www.rfc-editor.org/info/rfc7516>.

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

   [RFC7525]  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, <https://www.rfc-editor.org/info/rfc7525>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [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>.

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   [RFC8417]  Hunt, P., Ed., Jones, M., Denniss, W., and M. Ansari,
              "Security Event Token (SET)", RFC 8417,
              DOI 10.17487/RFC8417, July 2018,
              <https://www.rfc-editor.org/info/rfc8417>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

8.2.  Informative References

   [I-D.ietf-secevent-http-poll]
              Backman, A., Jones, M., Scurtescu, M., Ansari, M., and A.
              Nadalin, "Poll-Based Security Event Token (SET) Delivery
              Using HTTP", draft-ietf-secevent-http-poll-12 (work in
              progress), June 2020.

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

Appendix A.  Unencrypted Transport Considerations

   Earlier versions of this specification made the use of TLS optional
   and described security and privacy considerations resulting from use
   of unencrypted HTTP as the underlying transport.  When the working
   group decided to mandate usage HTTP over TLS, it also decided to
   preserve the description of these considerations in this non-
   normative appendix.

   SETs may contain sensitive information that is considered Personally
   Identifiable Information (PII).  In such cases, SET Transmitters and
   SET Recipients MUST protect the confidentiality of the SET contents.
   When TLS is not used, this means that the SET MUST be encrypted as
   described in JWE [RFC7516].

   If SETs were allowed to be transmitted over unencrypted channels,
   some privacy-sensitive information about them might leak, even though
   the SETs themselves are encrypted.  For instance, an attacker may be
   able to determine whether or not a SET was accepted and the reason
   for its rejection or may be able to derive information from being
   able to observe the size of the encrypted SET.  (Note that even when
   TLS is utilized, some information leakage is still possible; message
   padding algorithms to prevent side channels remain an open research
   topic.)

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Appendix B.  Other Streaming Specifications

   [[ NOTE TO THE RFC EDITOR: This section to be removed prior to
   publication ]]

   The following pub/sub, queuing, and streaming systems were reviewed
   as possible solutions or as input to the current draft:

   Poll-Based Security Event Token (SET) Delivery Using HTTP

   In addition to this specification, the WG is defining a polling-based
   SET delivery protocol.  That protocol [I-D.ietf-secevent-http-poll]
   describes it as:

   This specification defines how a series of Security Event Tokens
   (SETs) can be delivered to an intended recipient using HTTP POST over
   TLS initiated as a poll by the recipient.  The specification also
   defines how delivery can be assured, subject to the SET Recipient's
   need for assurance.

   XMPP Events

   The WG considered XMPP Events and their ability to provide a single
   messaging solution without the need for both polling and push modes.
   The feeling was the size and methodology of XMPP was too far apart
   from the current capabilities of the SECEVENTs community, which
   focuses in on HTTP based service delivery and authorization.

   Amazon Simple Notification Service

   Simple Notification Service is a pub/sub messaging product from AWS.
   SNS supports a variety of subscriber types: HTTP/HTTPS endpoints, AWS
   Lambda functions, email addresses (as JSON or plain text), phone
   numbers (via SMS), and AWS SQS standard queues.  It does not directly
   support pull, but subscribers can get the pull model by creating an
   SQS queue and subscribing it to the topic.  Note that this puts the
   cost of pull support back onto the subscriber, just as it is in the
   push model.  It is not clear that one way is strictly better than the
   other; larger, sophisticated developers may be happy to own message
   persistence so they can have their own internal delivery guarantees.
   The long tail of OIDC clients may not care about that or may fail to
   get it right.  Regardless, I think we can learn something from the
   Delivery Policies supported by SNS, as well as the delivery controls
   that SQS offers (e.g., Visibility Timeout, Dead-Letter Queues).  I am
   not suggesting that we need all of these things in the spec, but they
   give an idea of what features people have found useful.

   Other information:

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   o  API Reference:
      http://docs.aws.amazon.com/AWSSimpleQueueService/latest/
      APIReference/Welcome.html

   o  Visibility Timeouts:
      http://docs.aws.amazon.com/AWSSimpleQueueService/latest/
      SQSDeveloperGuide/sqs-visibility-timeout.html

   Apache Kafka

   Apache Kafka is an Apache open source project based upon TCP for
   distributed streaming.  It prescribes some interesting general-
   purpose features that seem to extend far beyond the simpler streaming
   model that SECEVENTs is after.  A comment from MS has been that Kafka
   does an acknowledge with poll combination event which seems to be a
   performance advantage.  See: https://kafka.apache.org/intro

   Google Pub/Sub

   The Google Pub Sub system favors a model whereby polling and
   acknowledgement of events is done with separate endpoints and as
   separate functions.

   Information:

   o  Cloud Overview - https://cloud.google.com/pubsub/

   o  Subscriber Overview - https://cloud.google.com/pubsub/docs/
      subscriber

   o  Subscriber Pull(poll) - https://cloud.google.com/pubsub/docs/pull

Appendix C.  Acknowledgments

   The editors would like to thank the members of the SCIM working
   group, which began discussions of provisioning events starting with
   draft-hunt-scim-notify-00 in 2015.  We would like to thank Phil Hunt
   and the other authors of draft-ietf-secevent-delivery-02, upon which
   this specification is based.  We would like to thank the participants
   in the SecEvents working group for their contributions to this
   specification.

   Additionally, we would like to thank the following individuals for
   their reviews of the specification: Joe Clarke, Roman Danyliw, Vijay
   Gurbani, Benjamin Kaduk, Erik Kline, Murray Kucherawy, Barry Leiba,
   Yaron Sheffer, Robert Sparks, Valery Smyslov, Eric Vyncke, and Robert
   Wilton.

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Appendix D.  Change Log

   [[ NOTE TO THE RFC EDITOR: This section to be removed prior to
   publication ]]

   Draft 00 - AB - Based on draft-ietf-secevent-delivery-02 with the
   following changes:

   o  Renamed to "Push-Based SET Token Delivery Using HTTP"

   o  Removed references to the HTTP Polling delivery method.

   o  Removed informative reference to RFC6202.

   Draft 01 - AB:

   o  Fixed area and workgroup to match secevent.

   o  Removed unused definitions and definitions already covered by SET.

   o  Renamed Event Transmitter and Event Receiver to SET Transmitter
      and SET Receiver, respectively.

   o  Added IANA registry for SET Delivery Error Codes.

   o  Removed enumeration of HTTP authentication methods.

   o  Removed generally applicable guidance for HTTP, authorization
      tokens, and bearer tokens.

   o  Moved guidance for using authentication methods as DoS protection
      to Security Considerations.

   o  Removed redundant instruction to use WWW-Authenticate header.

   o  Removed further generally applicable guidance for authorization
      tokens.

   o  Removed bearer token from example delivery request, and text
      referencing it.

   o  Broke delivery method description into separate request/response
      sections.

   o  Added missing empty line between headers and body in example
      request.

   o  Removed inapplicable notes about example formatting.

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   o  Removed text about SET creation and handling.

   o  Removed duplication in protocol description.

   o  Added "non-normative example" text to example transmission
      request.

   o  Fixed inconsistencies in use of Error Code term.

   Draft 02 - AB:

   o  Rewrote abstract and introduction.

   o  Rewrote definitions for SET Transmitter, SET Receiver.

   o  Renamed Event Delivery section to SET Delivery.

   o  Readability edits to Success Response and Failure Response
      sections.

   o  Consolidated definition of error response under Failure Response
      section.

   o  Removed Event Delivery Process section and moved its content to
      parent section.

   o  Readability edits to SET Delivery section and its subsections.

   o  Added callout that SET Receiver HTTP endpoint configuration is
      out-of-scope.

   o  Added callout that SET verification mechanisms are out-of-scope.

   o  Added retry guidance, notes regarding delivery reliability
      requirements.

   o  Added guidance around using JWS and/or JWE to authenticate
      persisted SETs.

   Draft 03 - mbj:

   o  Addressed problems identified in my 18-Jul-18 review message
      titled "Issues for both the Push and Poll Specs".

   o  Changes to align terminology with RFC 8417, for instance, by using
      the already defined term SET Recipient rather than SET Receiver.

   o  Applied editorial and minor normative corrections.

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   o  Updated Marius' contact information.

   Draft 04 - AB:

   o  Replaced Error Codes with smaller set of meaningfully
      differentiated codes.

   o  Added more error response examples.

   o  Removed un-referenced normative references.

   o  Added normative reference to JSON in error response definition.

   o  Added text clarifying that the value of the "description"
      attribute in error responses is implementation specific.

   o  Added requirement that error descriptions and responses are UTF-8
      encoded.

   o  Added error description language preferences and specification via
      "Accept-Language" and "Content-Language" headers.

   o  Added "recognized issuer" validation requirement in section 2.

   o  Added timeouts as an acceptable reason to resend a SET in section
      2.

   o  Edited text in section 1 to clarify that configuration is out of
      scope.

   o  Made minor editorial corrections.

   Draft 05 - AB:

   o  Made minor editorial corrections.

   o  Updated example request with a correct SET header and signature.

   o  Revised TLS guidance to allow implementers to provide
      confidentiality protection via JWE.

   o  Revised TLS guidance to require *at least* TLS 1.2.

   o  Revised TLS guidance to recommend supporting the newest version of
      TLS that meets security requirements.

   o  Revised SET Delivery Error Code format to allow the same set of
      characters as is allowed in error codes in RFC6749.

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   o  Added mention of HTTP Poll spec to list of other streaming specs
      in appendix.

   o  Added validation step requiring SET Recipient to verify that the
      SET is one which the SET Transmitter is expected to send to the
      SET Recipient.

   o  Changed responding to errors with an appropriate HTTP status code
      from optional to recommended.

   o  Changed Error Codes registry change policy from Expert Review to
      First Come First Served; added guidance that error codes are meant
      to be consumed by automated systems.

   o  Added text making clear that it is up to SET Recipients whether or
      not they will accept SETs where the SET Issuer is different from
      the SET Transmitter.

   o  Reworded guidance around signing and/or encrypting SETs for
      integrity protection.

   o  Renamed TLS "Support Considerations" section to "Confidentiality
      of SETs".

   o  Reworded guidance around subject identifier selection and privacy
      concerns.

   Draft 06 - mbj, MS:

   o  Made minor editorial corrections.

   o  Updated to indicate that failure response should be returned if
      errors occur in authenticating the SET.

   o  Updated reference for JSON from RFC 7159 to RFC 8259.

   o  Fixed Authentication Using Signed SETs to indicate the SET
      Transmitter must be authorized to deliver the SET, not the SET
      Issuer.

   o  Fixed Authenticating Persisted SETs to put the responsibility for
      ensuring the SET is signed on the SET Recipient.

   o  Fixed error code format definition to match error codes defined in
      doc.

   Draft 07 - AB:

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   o  Made minor editorial corrections.

   o  Removed "SET Recipient" definition and added explicit list of
      terms used from RFC8417.

   Draft 08 - mbj

   o  Addressed area director review comments by Benjamin Kaduk.

   Draft 09 - mbj + AB

   o  Corrected editorial nits.

   Draft 10 - AB

   o  Addressed area director review comments by Benjamin Kaduk:

      *  Added reference to 8417 as definition document for SETs.

      *  Added text clarifying that determining the SET Recipient's
         service identity is out of scope.

      *  Added normative recommendation for transmitters to target SETs
         to specific business needs of subscribers.

      *  Minor editorial corrections.

   Draft 11 - mbj

   o  Addressed SecDir review comments by Valery Smyslov.

   o  Addressed OpsDir review comments by Joe Clarke.

   o  Addressed GenArt review comments by Vijay Gurbani.

   Draft 12 - mbj

   o  Revised to unambiguously require the use of TLS, while preserving
      descriptions of precautions needed for non-TLS use in an appendix.

   Draft 13 - mbj

   o  Addressed IESG comments.

   Draft 14 - AB

   o  Revised normative requirements for SET re-transmission to clarify
      "at least once" delivery expectiations.

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   o  Added non-normative text to Section 4 - Delivery Reliability
      describing conditions where re-transmission of successfully
      delivered SETs may occur.

Authors' Addresses

   Annabelle Backman (editor)
   Amazon

   Email: richanna@amazon.com

   Michael B. Jones (editor)
   Microsoft

   Email: mbj@microsoft.com
   URI:   https://self-issued.info/

   Marius Scurtescu
   Coinbase

   Email: marius.scurtescu@coinbase.com

   Morteza Ansari
   Cisco

   Email: morteza.ansari@cisco.com

   Anthony Nadalin
   Microsoft

   Email: tonynad@microsoft.com

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