draft-jones-oauth-rfc7523bis.xml

<?xml version='1.0' encoding='UTF-8'?>
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<!DOCTYPE rfc PUBLIC "-//IETF//DTD RFC 2629//EN" "http://xml2rfc.tools.ietf.org/authoring/rfc2629.dtd">

<rfc xmlns:xi="http://www.w3.org/2001/XInclude"
  category="std" ipr="trust200902"
  docName="draft-jones-oauth-rfc7523bis-latest"
  obsoletes="7523" updates="7521, 7522, 9126">

  <?rfc toc="yes"?>
  <?rfc tocompact="yes"?>
  <?rfc tocdepth="5"?>
  <?rfc tocindent="yes"?>
  <?rfc symrefs="yes"?>
  <?rfc sortrefs="yes"?>
  <?rfc compact="yes"?>
  <?rfc subcompact="no"?>

  <front>
    <title abbrev="OAuth JWT Assertion Profiles">JSON Web Token (JWT) Profile for OAuth 2.0 Client Authentication and Authorization Grants</title>

    <author fullname="Michael B. Jones" surname="Jones" initials="M.B.">
      <organization>Self-Issued Consulting</organization>
      <address>
        <email>michael_b_jones@hotmail.com</email>
        <uri>https://self-issued.info/</uri>
      </address>
    </author>

    <author fullname="Brian Campbell" initials="B." surname="Campbell">
      <organization abbrev="Ping Identity">Ping Identity</organization>
      <address>
        <email>brian.d.campbell@gmail.com</email>
      </address>
    </author>

    <author fullname="Chuck Mortimore" initials="C." surname="Mortimore">
      <organization abbrev="Disney">Disney</organization>
      <address>
        <email>charliemortimore@gmail.com</email>
      </address>
    </author>

    <date day="25" month="November" year="2024" />

    <area>Security</area>
    <workgroup>OAuth Working Group</workgroup>

    <keyword>OAuth</keyword>
    <keyword>JWT</keyword>
    <keyword>Assertion</keyword>
    <keyword>Token</keyword>
    <keyword>Security Token</keyword>

    <abstract>
      <t>This specification defines the use of a JSON Web Token (JWT) Bearer Token as a means for
        requesting an OAuth 2.0 access token as well as for client authentication.
      </t>
    </abstract>
  </front>

  <middle>
    <section title="Introduction" anchor="Introduction">
      <t>
	JSON Web Token (JWT) <xref target="JWT"/>
	is a JSON-based <xref target="RFC8259"/> security token encoding
        that enables
	identity and security information to be shared across security
	domains.
        A security token is generally issued by an Identity Provider
        and consumed by a Relying Party that relies on its content to
        identify the token's subject for security-related purposes.
      </t>

      <t>
        The OAuth 2.0 Authorization Framework <xref target="RFC6749"/> provides
        a method for making authenticated HTTP requests to a resource using an access token.
        Access tokens are issued to third-party clients by an
        authorization server (AS) with the (sometimes implicit) approval of the resource owner.
        In OAuth, an authorization grant is an abstract term used to describe
        intermediate credentials that represent the resource owner
        authorization.  An authorization grant is used by the client to obtain an access token.
        Several authorization grant types are defined to support a wide range
        of client types and user experiences.
        OAuth also allows for the definition of new extension grant types
        to support additional clients or to provide a bridge between OAuth and other trust frameworks.
        Finally, OAuth allows the definition of additional authentication mechanisms to be used by clients when interacting with the authorization server.
      </t>

      <t>
	"Assertion Framework for OAuth 2.0 Client Authentication and Authorization Grants"
	<xref target="RFC7521"/>
	is an abstract extension to OAuth 2.0 that provides a general
        framework for the use of assertions (a.k.a. security tokens) as client credentials and/or authorization grants with OAuth 2.0.
        This specification profiles
	the OAuth Assertion Framework
	<xref target="RFC7521"/>
	to define an extension grant type that uses a JWT Bearer Token to
        request an OAuth 2.0 access token as well as for use as client credentials.
        The format and processing rules for the JWT defined in this specification are intentionally similar,
        though not identical, to those in the closely related specification "Security
	Assertion Markup Language (SAML) 2.0 Profile for OAuth 2.0 Client Authentication
        and Authorization Grants"
	<xref target="RFC7522"/>.
        The differences arise where the structure and semantics of JWTs differ from SAML Assertions.
        JWTs, for example, have no direct equivalent to the &lt;SubjectConfirmation&gt; or &lt;AuthnStatement&gt; elements of SAML Assertions.
      </t>

      <t>This document defines how a JWT Bearer Token can be used to request an access token when a client wishes to utilize an existing trust
        relationship, expressed through the semantics of
	the JWT,
        without a direct user-approval step at the authorization server.  It also defines how a JWT can be used as a client authentication mechanism.
        The use of a security token for client
        authentication is orthogonal to and separable from using a security token as an
        authorization grant.  They can be used either in combination or separately.
        Client authentication using a JWT is nothing more than an alternative way for a client to authenticate
        to the token endpoint or other endpoints
	such as the pushed authorization endpoint <xref target="RFC9126"/>
	and must be used in conjunction with some grant type to form a complete and
        meaningful protocol request. JWT authorization grants may be used with or without client authentication
        or identification. Whether or not client authentication is needed in conjunction with a JWT authorization
        grant, as well as the supported types of client authentication, are policy decisions at the discretion of the authorization server.
      </t>
      <t>The process by which the client obtains the JWT, prior to exchanging it with the authorization server or using it for client authentication, is out of scope.</t>

      <section title="Notational Conventions" anchor="NotationalConventions">
        <t>
	  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 <xref target="RFC2119"/> <xref target="RFC8174"/> when, and
	  only when, they appear in all capitals, as shown here.
	</t>
        <t>
          Unless otherwise noted, all the protocol parameter names and values are case sensitive.
        </t>
      </section>

      <section title='Terminology' anchor='Terminology'>
        <t>
	  All terms are as defined in the following specifications:
	  "The OAuth 2.0 Authorization Framework" <xref target="RFC6749"/>,
	  the OAuth Assertion Framework
	  <xref target="RFC7521"/>, and "JSON Web Token (JWT)" <xref target="JWT"/>.
        </t>
      </section>

    </section>

    <section title="HTTP Parameter Bindings for Transporting Assertions" anchor="Transporting">
      <t>
	The OAuth Assertion Framework
	<xref target="RFC7521"/>
	defines generic HTTP parameters for transporting assertions (a.k.a. security tokens)
	during interactions with a token endpoint.
	This section defines specific parameters and treatments of those parameters
	for use with JWT Bearer Tokens.
      </t>
      <section title="Using JWTs as Authorization Grants" anchor="AuthGrants">
	<t>
	  To use a Bearer JWT as an authorization grant, the client uses an access token request as defined in
	  Section 4 of
	  the OAuth Assertion Framework
	  <xref target="RFC7521"/>
	  with the following specific parameter values and encodings.
	</t>
	<t>The value of the <spanx style='verb'>grant_type</spanx> is
	<spanx style='verb'>urn:ietf:params:oauth:grant-type:jwt-bearer</spanx>.</t>
	<t>
	  The value of the <spanx style='verb'>assertion</spanx> parameter
	  MUST contain a single JWT.
	</t>
	<t>
	  The <spanx style='verb'>scope</spanx> parameter may be used, as defined in
	  the OAuth Assertion Framework
	  <xref target="RFC7521"/>, to indicate the requested scope.
	</t>
  <t>Authentication of the client is optional, as described in
   Section 3.2.1 of OAuth 2.0 <xref target="RFC6749"/> and
   consequently, the <spanx style='verb'>client_id</spanx> is only needed
   when a form of client authentication that relies on the parameter is used.</t>
  <t>The following example demonstrates an access token request with a JWT as an authorization grant
	(with extra line breaks for display purposes only):</t>

        <figure>
          <artwork><![CDATA[
  POST /token.oauth2 HTTP/1.1
  Host: as.example.com
  Content-Type: application/x-www-form-urlencoded

  grant_type=urn%3Aietf%3Aparams%3Aoauth%3Agrant-type%3Ajwt-bearer
  &assertion=eyJ0eXAiOiJhdXRob3JpemF0aW9uLWdyYW50K2p3dCIsImFsZyI6Ik
    VTMjU2Iiwia2lkIjoiMTYifQ.
  eyJhdWQiOiJodHRwczovLw[...omitted for brevity...].
  J9l-ZhwP[...omitted for brevity...]
]]></artwork>
        </figure>

      </section>
      <section title="Using JWTs for Client Authentication" anchor="ClientAuth">
	<t>To use a JWT Bearer Token for client authentication, the client uses the following parameter values and encodings.</t>
	<t>The value of the <spanx style='verb'>client_assertion_type</spanx> is
	<spanx style='verb'>urn:ietf:params:oauth:client-assertion-type:jwt-bearer</spanx>.</t>
	<t>
	  The value of the <spanx style='verb'>client_assertion</spanx> parameter
	  contains a single JWT. It MUST NOT contain more than one JWT.
  </t>

  <t>The following example demonstrates client
     authentication using a JWT during the presentation of an authorization code grant in an
     access token request
     (with extra line breaks for display purposes only):</t>

        <figure>
          <artwork><![CDATA[
  POST /token.oauth2 HTTP/1.1
  Host: as.example.com
  Content-Type: application/x-www-form-urlencoded

  grant_type=authorization_code&
  code=n0esc3NRze7LTCu7iYzS6a5acc3f0ogp4&
  client_assertion_type=urn%3Aietf%3Aparams%3Aoauth%3A
  client-assertion-type%3Ajwt-bearer&
  client_assertion=eyJ0eXAiOiJjbGllbnQtYXV0aGVudGljYXRpb24rand0Iiwi
    YWxnIjoiUlMyNTYiLCJraWQiOiIyMiJ9.
  eyJhdWQiOiJodHRwczovLw[...omitted for brevity...].
  cC4hiUPo[...omitted for brevity...]
]]></artwork>
        </figure>

      </section>
    </section>

    <section title="JWT Format and Processing Requirements" anchor="Processing">
      <t>
	In order to issue an access token response as described in
	OAuth 2.0 <xref target="RFC6749"/>
	or to rely on a JWT for client authentication,
	the authorization server MUST validate the JWT according to the criteria below.
	Application of additional restrictions and policy are at the discretion of the authorization server.
      </t>
      <t>
	<list style="numbers">

	  <t>
	    The JWT MUST be explicitly typed,
	    as defined in Section 3.11 of <xref target="RFC8725"/>.
	    The <spanx style="verb">typ</spanx> header parameter values
	    that MUST be used are defined in <xref target="GrantProcessing"/>
	    and <xref target="ClientProcessing"/>.
	    The authorization server MUST reject JWTs that do not use
	    the specified explicit type value.
	  </t>
	  <t>
	    The JWT MUST contain an <spanx style="verb">iss</spanx>
	    (issuer) claim that contains a unique identifier for the
	    entity that issued the JWT.
	    In the absence of an application profile specifying
	    otherwise, compliant applications MUST compare issuer
	    values using the Simple String Comparison method defined in Section
	    6.2.1 of RFC 3986 <xref target="RFC3986"/>.
	  </t>
	  <t>
	    The JWT MUST contain a <spanx style="verb">sub</spanx>
	    (subject) claim identifying the
	    principal that is the subject of the JWT. Two cases need to
	    be differentiated:
      <list style="letters">
        <t> For the authorization grant, the subject typically identifies an authorized accessor for which the
            access token is being requested (i.e., the resource owner or an authorized delegate), but
            in some cases, may be a pseudonymous identifier or other value denoting an anonymous user.</t>

        <t>
	  For client authentication, the subject MUST be the
          <spanx style='verb'>client_id</spanx> of the OAuth client.
        </t>
      </list>
	  </t>
	  <t>
	    The JWT MUST contain an <spanx style="verb">aud</spanx>
	    (audience) claim containing
	    the issuer identifier <xref target="RFC8414"/>
	    of the authorization server as its sole value.
	    The authorization server MUST have an issuer identifier
	    to be used with this specification.
	    Unlike the <spanx style="verb">aud</spanx> value specified
	    in <xref target="RFC7523"/>, there MUST be no value other than
	    the issuer identifier of the intended authorization server
	    used as the audience of the JWT;
	    this includes that the token endpoint URL of the authorization server
	    MUST NOT be used as an audience value.
	    To simplify implementations,
	    the <spanx style="verb">aud</spanx> claim value MUST
	    be a JSON string, and not a single-valued JSON array.
	    The authorization server MUST reject any JWT that does not
	    contain its issuer identifier as its sole audience value.
	    In the absence of an application profile specifying
	    otherwise, compliant applications MUST compare the audience
	    values using the Simple String Comparison method defined in Section
	    6.2.1 of RFC 3986 <xref target="RFC3986"/>.
	  </t>
	  <t>
	    The JWT MUST contain an <spanx style="verb">exp</spanx>
	    (expiration time) claim that limits the time window during
	    which the JWT can be used.  The authorization server
	    MUST reject any JWT with an expiration time that has passed,
	    subject to allowable clock skew between systems.
            Note that the
	    authorization server may reject JWTs with an <spanx
	    style="verb">exp</spanx> claim value that is
	    unreasonably far in the future.
	  </t>
	  <t>
	    The JWT MAY contain an <spanx style="verb">nbf</spanx>
	    (not before) claim that identifies the time before which
	    the token MUST NOT be accepted for processing.
	  </t>
	  <t>
	    The JWT MAY contain an <spanx style="verb">iat</spanx>
	    (issued at) claim that identifies the time at which the
	    JWT was issued.  Note that the authorization server may reject JWTs
	    with an <spanx style="verb">iat</spanx> claim value that is
	    unreasonably far in the past.
	  </t>
	  <t>
	    The JWT MAY contain a <spanx style="verb">jti</spanx>
	    (JWT ID) claim that provides a unique identifier for
	    the token.
	    The authorization server MAY ensure that JWTs are not
	    replayed by maintaining the set of used
	    <spanx style="verb">jti</spanx> values for the length of
	    time for which the JWT would be considered valid based
	    on the applicable <spanx style="verb">exp</spanx> instant.
	  </t>
	  <t>
	    The JWT MAY contain other claims.
	  </t>
	  <t>
	    The JWT MUST be digitally signed or have a Message Authentication Code (MAC) applied
      by the issuer.  The authorization server
      MUST reject JWTs with an invalid signature or MAC.
	  </t>
	  <t>
	    The authorization server MUST reject a JWT that is not
	    valid in all other respects per
	    "JSON Web Token (JWT)" <xref target="JWT"/>.
	  </t>
	</list>
      </t>

      <section title="Authorization Grant Processing" anchor="GrantProcessing">

	<t>
	  Authorization grant JWTs MUST be explicitly typed by using the
	  <spanx style="verb">typ</spanx> header parameter value
	  <spanx style="verb">authorization-grant+jwt</spanx> or
	  another more specific explicit type value defined by a specification profiling this specification.
	  Authorization grant JWTs not using the explicit type value
	  MUST be rejected by the authorization server.
	</t>
	<t>
	  JWT authorization grants may be used with or without client authentication
	  or identification. Whether or not client authentication is needed in
	  conjunction with a JWT authorization grant, as well as the supported types
	  of client authentication, are policy decisions at the discretion of the
	  authorization server. However, if client credentials are present in
	  the request, the authorization server MUST validate them.
	</t>

	<t>If the JWT is not valid, or the current time is not within the token's valid time window for use, the
	authorization server constructs an error response as defined in
	OAuth 2.0 <xref target="RFC6749"/>.
	The value of the <spanx style='verb'>error</spanx> parameter MUST be the
	<spanx style='verb'>invalid_grant</spanx> error code.  The authorization server
	MAY include additional information regarding the reasons the JWT was considered invalid using the
	<spanx style='verb'>error_description</spanx> or <spanx style='verb'>error_uri</spanx> parameters.
	<figure>
	  <preamble>For example:</preamble>
	  <artwork><![CDATA[
  HTTP/1.1 400 Bad Request
  Content-Type: application/json
  Cache-Control: no-store

  {
   "error":"invalid_grant",
   "error_description":"Audience validation failed"
  }
]]></artwork>
	</figure>
	</t>
      </section>

      <section title="Client Authentication Processing" anchor="ClientProcessing">

	<t>
	  Client authentication JWTs MUST be explicitly typed by using the
	  <spanx style="verb">typ</spanx> header parameter value
	  <spanx style="verb">client-authentication+jwt</spanx>
	  another more specific explicit type value defined by a specification profiling this specification.
	  Client authentication JWTs not using the explicit type value
	  MUST be rejected by the authorization server.
	</t>
	<t>If the client JWT is not valid, the
	authorization server constructs an error response as defined in
	OAuth 2.0 <xref target="RFC6749"/>.
	The value of the <spanx style='verb'>error</spanx> parameter MUST be the
	<spanx style='verb'>invalid_client</spanx> error code.  The authorization server
	MAY include additional information regarding the reasons the JWT was considered invalid using the
	<spanx style='verb'>error_description</spanx> or <spanx style='verb'>error_uri</spanx> parameters.
	</t>
      </section>
    </section>

    <section title="Authorization Grant Example" anchor="GrantExample">
      <t>The following examples illustrate what a conforming JWT and an access token request would look like.
      </t>
      <t>
	The example shows a JWT issued and signed by the system entity identified as
	<spanx style='verb'>https://jwt-idp.example.com</spanx>.
	The subject of the JWT is identified by email address as <spanx style='verb'>mike@example.com</spanx>.
	The intended audience of the JWT is <spanx style='verb'>https://authz.example.net</spanx>,
	which is the authorization server's issuer identifier.
	The JWT is sent as part of an access token request to the authorization server's
	token endpoint at <spanx style='verb'>https://authz.example.net/token.oauth2</spanx>.
      </t>
      <figure>
	<preamble>
	  Below is an example JSON object that could be encoded to
	  produce the JWT Claims Set for a JWT:
	</preamble>
	<artwork><![CDATA[
  {"aud":"https://authz.example.net",
   "iss":"https://jwt-idp.example.com",
   "sub":"mailto:mike@example.com",
   "iat":1731721541,
   "exp":1731725141,
   "http://claims.example.com/member":true
  }
]]></artwork>
      </figure>

      <figure>
	<preamble>
	  The following example JSON object, used as the header parameters of a JWT,
	  declares that the JWT is an authorization grant JWT,
	  is signed with the Elliptic Curve Digital Signature Algorithm (ECDSA) P-256 with SHA-256,
	  and was signed with a key identified by
	  the <spanx style="verb">kid</spanx> value <spanx style="verb">16</spanx>.
	</preamble>
	<artwork><![CDATA[
  {"typ":"authorization-grant+jwt","alg":"ES256","kid":"16"}
]]></artwork>
      </figure>

      <figure>
	<preamble>
	  To present the JWT with the claims and header shown in the previous example as part of an access token request, for example,
	  the client might make the following HTTPS request
	  (with extra line breaks for display purposes only):
	</preamble>
	<artwork><![CDATA[
  POST /token.oauth2 HTTP/1.1
  Host: authz.example.net
  Content-Type: application/x-www-form-urlencoded

  grant_type=urn%3Aietf%3Aparams%3Aoauth%3Agrant-type%3Ajwt-bearer
  &assertion=eyJ0eXAiOiJhdXRob3JpemF0aW9uLWdyYW50K2p3dCIsImFsZyI6Ik
    VTMjU2Iiwia2lkIjoiMTYifQ.
  eyJhdWQiOiJodHRwczovLw[...omitted for brevity...].
  J9l-ZhwP[...omitted for brevity...]
]]></artwork>
      </figure>
    </section>

    <section anchor="Interoperability" title="Interoperability Considerations">

      <t>
	Agreement between system entities regarding identifiers,
	keys, and endpoints is required in order to achieve interoperable
	deployments of this profile. Specific items that require agreement include
	values for the issuer identifiers, the locations of endpoints, the key used to
	apply and verify the digital signature or MAC over the JWT, one-time use restrictions on the JWT,
  maximum JWT lifetime allowed, and the specific subject and claim requirements of the JWT.
	The exchange of such information is explicitly out of scope for this specification.
	In some cases, additional profiles may be created that constrain or prescribe these values or specify
	how they are to be exchanged.
	Examples of such profiles include
	the OAuth 2.0 Dynamic Client Registration Protocol <xref target="RFC7591"/>,
	OAuth 2.0 Authorization Server Metadata <xref target="RFC8414"/>,
	OpenID Connect Dynamic Client Registration 1.0 <xref target="OpenID.Registration"/>,
	OpenID Connect Discovery 1.0 <xref target="OpenID.Discovery"/>,
	and OpenID Federation 1.0  <xref target="OpenID.Federation"/>.
      </t>
      <t>
        The <spanx style="verb">RS256</spanx> algorithm, from <xref target="JWA"/>, is a mandatory-to-implement JSON Web
        Signature algorithm for this profile.
      </t>

    </section>

    <section anchor="Security" title="Security Considerations">

      <t>
       The security considerations described within the following specifications are all applicable
       to this document:
       "Assertion Framework for OAuth 2.0 Client Authentication and Authorization Grants"
       <xref target="RFC7521"/>,
       "The OAuth 2.0 Authorization Framework" <xref target="RFC6749"/>, and "JSON Web Token (JWT)" <xref target="JWT"/>.
      </t>
      <t>
        The specification does not mandate replay protection for the JWT
        usage for either the authorization grant or for client
        authentication. It is an optional feature, which implementations may employ at their own discretion.
     </t>
     <t>
       This specification tightens the JWT audience requirements to prevent attacks
       that could result from exploiting audience ambiguities
       allowed by <xref target="RFC7523"/>.
     </t>

    </section>
    <section anchor="Privacy" title="Privacy Considerations">

      <t>
        A JWT may contain privacy-sensitive information and, to prevent disclosure of such information to unintended parties,
        should only be transmitted over encrypted channels, such as Transport Layer Security (TLS). In cases where it is desirable to prevent disclosure
        of certain information to the client, the JWT should be encrypted to the authorization server.
      </t>
      <t>
        Deployments should determine the minimum amount of information necessary to complete the exchange and include
        only such claims in the JWT. In some cases, the <spanx style="verb">sub</spanx> (subject) claim can be a value representing an anonymous
        or pseudonymous user, as described in Section 6.3.1 of
	the OAuth Assertion Framework
	<xref target="RFC7521"/>.
      </t>
    </section>

    <section title='IANA Considerations' anchor="IANA">
      <t>
	The IANA actions of registering the URNs
	<spanx style="verb">urn:ietf:params:oauth:grant-type:jwt-bearer</spanx>
	and
	<spanx style="verb">urn:ietf:params:oauth:client-assertion-type:jwt-bearer</spanx>
	in the IANA "OAuth URI" registry <xref target="IANA.OAuth.Parameters"/>
	established by
	"An IETF URN Sub-Namespace for OAuth" <xref target="RFC6755"/>
	were performed by <xref target="RFC7523"/>.
      </t>

      <section title="Media Type Registration" anchor="MediaReg">
        <t>
          This section registers the following media types <xref target="RFC2046"/>
          in the "Media Types" registry <xref target="IANA.MediaTypes"/>
          in the manner described in <xref target="RFC6838"/>.
        </t>

        <section title="Registry Contents" anchor="MediaContents">
          <t>
            <?rfc subcompact="yes"?>
            <list style="symbols">
              <t>
                Type name: application
              </t>
              <t>
                Subtype name: authorization-grant+jwt
              </t>
              <t>
                Required parameters: n/a
              </t>
              <t>
                Optional parameters: n/a
              </t>
              <t>
                Encoding considerations: binary;
                An authorization grant JWT is a JWT;
                JWT values are encoded as a
                series of base64url-encoded values (some of which may be the
                empty string) separated by period ('.') characters.
              </t>
              <t>
                Security considerations: See <xref target="Security"/> of this specification
              </t>
              <t>
                Interoperability considerations: n/a
              </t>
              <t>
                Published specification: <xref target="GrantProcessing"/> of this specification
              </t>
              <t>
                Applications that use this media type:
                Applications that use this specification
              </t>
              <t>
                Fragment identifier considerations: n/a
              </t>
              <t>
                Additional information:<list style="empty">
                <t>Magic number(s): n/a</t>
                <t>File extension(s): n/a</t>
                <t>Macintosh file type code(s): n/a </t></list>
                <vspace/>
              </t>
              <t>
                Person &amp; email address to contact for further information:
                <vspace/>
                Michael B. Jones, michael_b_jones@hotmail.com
              </t>
              <t>
                Intended usage: COMMON
              </t>
              <t>
                Restrictions on usage: none
              </t>
              <t>
                Author: Michael B. Jones, michael_b_jones@hotmail.com
              </t>
              <t>
                Change controller: OpenID Foundation Artifact Binding Working Group - openid-specs-ab@lists.openid.net
              </t>
              <t>
                Provisional registration? No
              </t>
            </list>
            <?rfc subcompact="no"?>
          </t>

          <t>
            <?rfc subcompact="yes"?>
            <list style="symbols">
              <t>
                Type name: application
              </t>
              <t>
                Subtype name: client-authentication+jwt
              </t>
              <t>
                Required parameters: n/a
              </t>
              <t>
                Optional parameters: n/a
              </t>
              <t>
                Encoding considerations: binary;
                A client authentication JWT is a JWT;
                JWT values are encoded as a
                series of base64url-encoded values (some of which may be the
                empty string) separated by period ('.') characters.
              </t>
              <t>
                Security considerations: See <xref target="Security"/> of this specification
              </t>
              <t>
                Interoperability considerations: n/a
              </t>
              <t>
                Published specification: <xref target="ClientProcessing"/> of this specification
              </t>
              <t>
                Applications that use this media type:
                Applications that use this specification
              </t>
              <t>
                Fragment identifier considerations: n/a
              </t>
              <t>
                Additional information:<list style="empty">
                <t>Magic number(s): n/a</t>
                <t>File extension(s): n/a</t>
                <t>Macintosh file type code(s): n/a </t></list>
                <vspace/>
              </t>
              <t>
                Person &amp; email address to contact for further information:
                <vspace/>
                Michael B. Jones, michael_b_jones@hotmail.com
              </t>
              <t>
                Intended usage: COMMON
              </t>
              <t>
                Restrictions on usage: none
              </t>
              <t>
                Author: Michael B. Jones, michael_b_jones@hotmail.com
              </t>
              <t>
                Change controller: OpenID Foundation Artifact Binding Working Group - openid-specs-ab@lists.openid.net
              </t>
              <t>
                Provisional registration? No
              </t>
            </list>
            <?rfc subcompact="no"?>
          </t>
        </section>

      </section>
    </section>

    <section title="Updates to RFC 7521" anchor="RFC7521Updates">
      <t>
	This section updates
	"Assertion Framework for OAuth 2.0 Client Authentication and
	Authorization Grants" <xref target="RFC7521"/>
	to tighten its audience requirements.
      </t>
      <t>
	The description of the Audience parameter
	in Section 5.1 of <xref target="RFC7521"/> (Assertion Metamodel)
	is replaced by:
	<list style="hanging">

	  <t hangText="Audience">
	    <vspace/>
            A value that identifies the party intended to process the assertion.
	    The audience MUST contain the issuer identifier <xref target="RFC8414"/>
	    of the authorization server as its sole value.
	    Unlike the audience value specified
	    in <xref target="RFC7521"/>, there MUST be no value other than
	    the issuer identifier of the intended authorization server
	    used as the audience of the assertion;
	    this includes that the token endpoint URL of the authorization server
	    MUST NOT be used as an audience value.
	  </t>
	</list>
      </t>
      <t>
	The description of the Audience parameter
	in Section 5.2 of <xref target="RFC7521"/> (General Assertion Format and Processing Rules)
	is replaced by:
	<list style="symbols">
	  <t>
	    The assertion MUST contain an audience that identifies the
            authorization server as the intended audience,
	    with the issuer identifier <xref target="RFC8414"/>
	    of the authorization server as its sole value.
            The authorization server MUST reject any assertion that does not
            contain its own issuer identifier as the sole audience value.
	  </t>
	</list>
      </t>
      <t>
	In the list of agreements required by participants
	in Section 7 of <xref target="RFC7521"/> (Interoperability Considerations),
	"Audience identifiers" is removed from the list.
      </t>
    </section>

    <section title="Updates to RFC 7522" anchor="RFC7522Updates">
      <t>
	This section updates
	"Security Assertion Markup Language (SAML) 2.0 Profile for OAuth 2.0
	Client Authentication and Authorization Grants" <xref target="RFC7522"/>
	to tighten its audience requirements.
      </t>
      <t>
	The description of the Audience element in Item 2 of
	Section 3 of <xref target="RFC7522"/> (Assertion Format and Processing Requirements)
	is replaced by:
	<list style="empty">
	  <t>
	    The Assertion MUST contain a &lt;Conditions&gt; element
	    with an &lt;AudienceRestriction&gt; element
	    with a single &lt;Audience&gt; element that identifies the
	    authorization server as the intended audience.
	    The value of the &lt;Audience&gt; element MUST be
	    the issuer identifier <xref target="RFC8414"/> of the authorization server.
	    Section 2.5.1.4 of
	    "Assertions and Protocols for the OASIS Security Assertion Markup Language (SAML) V2.0"
	    <xref target="OASIS.saml-core-2.0-os"/>
	    defines the &lt;AudienceRestriction&gt; and &lt;Audience&gt; elements.
	    Unlike the audience value specified in <xref target="RFC7522"/>,
	    there MUST be no value other than
	    the issuer identifier of the intended authorization server
	    used as the audience of the assertion;
	    this includes that the token endpoint URL of the authorization server
	    MUST NOT be used as an audience value.
	    <vspace blankLine="1"/>

	    The authorization server MUST reject any assertion that does not
	    contain its own issuer identifier as the sole audience value.
	  </t>
	</list>
      </t>
      <t>
	In Section 4 of <xref target="RFC7522"/> (Authorization Grant Example),
	the sentence:
	<list style="empty">
	  <t>
	    The intended audience of the Assertion is
	    <spanx style='verb'>https://saml-sp.example.net</spanx>,
	    which is an identifier for a SAML Service Provider
	    with which the authorization server identifies itself.
	  </t>
	</list>
	is replaced by:
	<list style="empty">
	  <t>
	    The intended audience of the Assertion is
	    <spanx style='verb'>https://authz.example.net</spanx>,
	    which is the authorization server's issuer identifier.
	  </t>
	</list>
      </t>
      <figure title='Example SAML 2.0 Assertion' anchor='assertion'>
	<preamble>
	  In the same section, the SAML 2.0 Assertion example is replaced by:
	</preamble>
	<artwork><![CDATA[
  <Assertion IssueInstant="2024-11-17T00:53:34.619Z"
    ID="ef1xsbZxPV2oqjd7HTLRLIBlBb7"
    Version="2.0"
    xmlns="urn:oasis:names:tc:SAML:2.0:assertion">
   <Issuer>https://saml-idp.example.com</Issuer>
   <ds:Signature xmlns:ds="http://www.w3.org/2000/09/xmldsig#">
    [...omitted for brevity...]
   </ds:Signature>
   <Subject>
    <NameID
     Format="urn:oasis:names:tc:SAML:1.1:nameid-format:emailAddress">
     brian@example.com
    </NameID>
    <SubjectConfirmation
      Method="urn:oasis:names:tc:SAML:2.0:cm:bearer">
     <SubjectConfirmationData
       NotOnOrAfter="2024-11-17T00:58:34.619Z"
       Recipient="https://authz.example.net/token.oauth2"/>
     </SubjectConfirmation>
    </Subject>
    <Conditions>
      <AudienceRestriction>
        <Audience>https://authz.example.net</Audience>
      </AudienceRestriction>
    </Conditions>
    <AuthnStatement AuthnInstant="2024-11-17T00:53:34.371Z">
      <AuthnContext>
        <AuthnContextClassRef>
          urn:oasis:names:tc:SAML:2.0:ac:classes:X509
        </AuthnContextClassRef>
      </AuthnContext>
    </AuthnStatement>
  </Assertion>
]]></artwork>
      </figure>
      <t>
	In the list of agreements required by participants
	in Section 5 of <xref target="RFC7521"/> (Interoperability Considerations),
	"Audience identifiers" is removed from the list.
      </t>
    </section>

    <section title="Updates to RFC 9126" anchor="RFC9126Updates">
      <t>
	This section updates
	"OAuth 2.0 Pushed Authorization Requests" <xref target="RFC9126"/>
	to tighten its audience requirements.
      </t>
      <t>
	The paragraph describing the audience value
	in Section 2 of <xref target="RFC9126"/> (Pushed Authorization Request Endpoint)
	is replaced by:
	<list style="empty">
	  <t>
	    This update resolves the potential ambiguity regarding
	    the appropriate audience value to use when employing
	    JWT client assertion-based authentication
	    (as defined in Section 2.2 of <xref target="RFC7523"/> with the
	    <spanx style="verb">private_key_jwt</spanx> or
	    <spanx style="verb">client_secret_jwt</spanx> authentication method names
	    per Section 9 of <xref target="OpenID.Core"/>)
	    that was described in <xref target="RFC9126"/>.
	    To address that ambiguity, the issuer identifier URL
	    of the authorization server according to <xref target="RFC8414"/>
	    MUST be used as the sole value of the audience.
            The authorization server MUST reject any such JWT that does not
            contain its own issuer identifier as the sole audience value.
	  </t>
	</list>
      </t>
    </section>

  </middle>

  <back>

    <references title="Normative References">

      <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.2119.xml"/>
      <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.3986.xml"/>
      <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6749.xml"/>
      <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7521.xml"/>
      <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7522.xml"/>
      <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7523.xml"/>
      <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8174.xml"/>
      <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8259.xml"/>
      <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8414.xml"/>
      <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8725.xml"/>
      <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9126.xml"/>

      <!-- Reference from https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7518.xml with change to anchor="JWA" -->

      <reference anchor="JWA" target="https://www.rfc-editor.org/info/rfc7518">
	<front>
	  <title>JSON Web Algorithms (JWA)</title>
	  <author fullname="M. Jones" initials="M." surname="Jones"/>
	  <date month="May" year="2015"/>
	  <abstract>
	    <t>This specification registers cryptographic algorithms and identifiers to be used with the JSON Web Signature (JWS), JSON Web Encryption (JWE), and JSON Web Key (JWK) specifications. It defines several IANA registries for these identifiers.</t>
	  </abstract>
	</front>
	<seriesInfo name="RFC" value="7518"/>
	<seriesInfo name="DOI" value="10.17487/RFC7518"/>
      </reference>

      <!-- Reference from https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7519.xml with change to anchor="JWT" -->

      <reference anchor="JWT" target="https://www.rfc-editor.org/info/rfc7519">
	<front>
	  <title>JSON Web Token (JWT)</title>
	  <author fullname="M. Jones" initials="M." surname="Jones"/>
	  <author fullname="J. Bradley" initials="J." surname="Bradley"/>
	  <author fullname="N. Sakimura" initials="N." surname="Sakimura"/>
	  <date month="May" year="2015"/>
	  <abstract>
	    <t>JSON Web Token (JWT) is a compact, URL-safe means of representing claims to be transferred between two parties. The claims in a JWT are encoded as a JSON object that is used as the payload of a JSON Web Signature (JWS) structure or as the plaintext of a JSON Web Encryption (JWE) structure, enabling the claims to be digitally signed or integrity protected with a Message Authentication Code (MAC) and/or encrypted.</t>
	  </abstract>
	</front>
	<seriesInfo name="RFC" value="7519"/>
	<seriesInfo name="DOI" value="10.17487/RFC7519"/>
      </reference>

      <reference target="https://docs.oasis-open.org/security/saml/v2.0/saml-core-2.0-os.pdf" anchor="OASIS.saml-core-2.0-os">
	<front><title>Assertions and Protocols for the OASIS Security Assertion Markup Language
	(SAML) V2.0</title>
	<author fullname="Scott Cantor" initials="S." surname="Cantor">
	  <organization>Internet2</organization>
	<address><email>cantor.2@osu.edu</email></address></author>
	<author fullname="John Kemp" initials="J." surname="Kemp"><organization>Nokia</organization>
	<address><email>John.Kemp@nokia.com</email></address></author><author fullname="Rob Philpott" initials="R." surname="Philpott">
	<organization>RSA Security</organization>
	<address><email>rphilpott@rsasecurity.com</email></address></author>
	<author fullname="Eve Maler" initials="E." surname="Maler">
	<organization>Sun Microsystems</organization><address><email>eve.maler@sun.com</email></address></author>
	<date year="2005" month="March"/></front>
	<seriesInfo name="OASIS Standard" value="saml-core-2.0-os"/>
      </reference>

    </references>

    <references title="Informative References">
      <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.2046.xml"/>
      <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6755.xml"/>
      <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6838.xml"/>
      <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7591.xml"/>

      <reference anchor="OpenID.Core" target="https://openid.net/specs/openid-connect-core-1_0.html">
	<front>
	  <title>OpenID Connect Core 1.0 incorporating errata set 2</title>

	  <author fullname="Nat Sakimura" initials="N." surname="Sakimura">
	    <organization abbrev="NAT.Consulting (was at NRI)">NAT.Consulting</organization>
	  </author>

	  <author fullname="John Bradley" initials="J." surname="Bradley">
	    <organization abbrev="Yubico (was at Ping Identity)">Yubico</organization>
	  </author>

	  <author fullname="Michael B. Jones" initials="M.B." surname="Jones">
	    <organization abbrev="Self-Issued Consulting (was at Microsoft)">Self-Issued Consulting</organization>
	  </author>

	  <author fullname="Breno de Medeiros" initials="B." surname="de Medeiros">
	    <organization abbrev="Google">Google</organization>
	  </author>

	  <author fullname="Chuck Mortimore" initials="C." surname="Mortimore">
	    <organization abbrev="Disney (was at Salesforce)">Disney</organization>
	  </author>

	  <date day="15" month="December" year="2023"/>
	</front>
      </reference>

      <reference anchor="OpenID.Registration" target="https://openid.net/specs/openid-connect-registration-1_0.html">
	<front>
	  <title>OpenID Connect Dynamic Client Registration 1.0 incorporating errata set 2</title>
	  <author fullname="Nat Sakimura" initials="N." surname="Sakimura">
	    <organization abbrev="NAT.Consulting (was at NRI)">NAT.Consulting</organization>
	  </author>
	  <author fullname="John Bradley" initials="J." surname="Bradley">
	    <organization abbrev="Yubico (was at Ping Identity)">Yubico</organization>
	  </author>
	  <author fullname="Michael B. Jones" initials="M.B." surname="Jones">
	    <organization abbrev="Self-Issued Consulting (was at Microsoft)">Self-Issued Consulting</organization>
	  </author>
	  <date day="15" month="December" year="2023"/>
	</front>
      </reference>

      <reference anchor="OpenID.Discovery" target="https://openid.net/specs/openid-connect-discovery-1_0.html">
	<front>
	  <title>OpenID Connect Discovery 1.0 incorporating errata set 2</title>
	  <author fullname="Nat Sakimura" initials="N." surname="Sakimura">
	    <organization abbrev="NAT.Consulting (was at NRI)">NAT.Consulting</organization>
	  </author>
	  <author fullname="John Bradley" initials="J." surname="Bradley">
	    <organization abbrev="Yubico (was at Ping Identity)">Yubico</organization>
	  </author>
	  <author fullname="Michael B. Jones" initials="M.B." surname="Jones">
	    <organization abbrev="Self-Issued Consulting (was at Microsoft)">Self-Issued Consulting</organization>
	  </author>
	  <author fullname="Edmund Jay" initials="E." surname="Jay">
	    <organization abbrev="Illumila">Illumila</organization>
	  </author>
	  <date day="15" month="December" year="2023"/>
	</front>
      </reference>

      <reference anchor="OpenID.Federation" target="https://openid.net/specs/openid-federation-1_0.html">
	<front>
	  <title>OpenID Federation 1.0</title>
	  <author fullname="Roland Hedberg">
	    <organization>independent</organization>
	  </author>
	  <author fullname="Michael B. Jones">
	    <organization>Self-Issued Consulting</organization>
	  </author>
	  <author fullname="A. Solberg">
	    <organization>Sikt</organization>
	  </author>
	  <author fullname="John Bradley">
	    <organization>Yubico</organization>
	  </author>
	  <author fullname="Giuseppe De Marco">
	    <organization>independent</organization>
	  </author>
	  <author fullname="Vladimir Dzhuvinov">
	    <organization>Connect2id</organization>
	  </author>
	  <date day="24" month="October" year="2024"/>
	</front>
      </reference>

      <reference anchor="IANA.OAuth.Parameters" target="https://www.iana.org/assignments/oauth-parameters">
	<front>
	  <title>OAuth Parameters</title>
	  <author>
	    <organization>IANA</organization>
	  </author>
	  <date/>
	</front>
      </reference>

      <reference anchor="IANA.MediaTypes" target="https://www.iana.org/assignments/media-types">
	<front>
	  <title>Media Types</title>
	  <author>
	    <organization>IANA</organization>
	  </author>
	  <date/>
	</front>
      </reference>

    </references>

    <section title="Document History" anchor="History">
      <t>
	[[ to be removed by the RFC Editor before publication as an RFC ]]
      </t>

      <t>
	-00
	<list style="symbols">
	  <t>
	    Initial draft starting with rfc7523.xml,
	    updated to use current references and affiliations
	    and modern xml2rfc syntax,
	    removing the IANA actions already performed,
	    and adding the Document History section.
	  </t>
	  <t>
	    Use AS issuer identifier as the sole audience value.
	  </t>
	  <t>
	    Explicitly typed authorization grant JWTs and client authentication JWTs.
	  </t>
	  <t>
	    Update audience requirements in
	    "Assertion Framework for OAuth 2.0 Client Authentication and
	    Authorization Grants" <xref target="RFC7521"/>.
	  </t>
	  <t>
	    Update audience requirements in
	    "Security Assertion Markup Language (SAML) 2.0 Profile for OAuth 2.0
	    Client Authentication and Authorization Grants" <xref target="RFC7522"/>.
	  </t>
	  <t>
	    Update audience requirements in
	    "OAuth 2.0 Pushed Authorization Requests" <xref target="RFC9126"/>.
	  </t>
	</list>
      </t>

    </section>

    <section title='Acknowledgements' anchor='Acknowledgements' numbered="no">
      <t>
	The profile in <xref target="RFC7523"/> was derived from
	"Security Assertion Markup Language (SAML) 2.0 Profile for OAuth 2.0 Client Authentication and Authorization Grants"
	<xref target="RFC7522"/>,
	which has the same authors as this document.
      </t>
      <t>
	We would like to acknowledge the contributions of the following
	people to this specification:
	John Bradley,
	Ralph Bragg,
	Joseph Heenan,
	Pedram Hosseyni,
	Aaron Parecki,
	Filip Skokan,
	and
	Tim Würtele.
      </t>
    </section>

  </back>
</rfc>