



Internet Engineering Task Force (IETF)                       V. Bertocci
Request for Comments: 9068                                         Auth0
Category: Standards Track                                   October 2021
ISSN: 2070-1721


        JSON Web Token (JWT) Profile for OAuth 2.0 Access Tokens

Abstract

   This specification defines a profile for issuing OAuth 2.0 access
   tokens in JSON Web Token (JWT) format.  Authorization servers and
   resource servers from different vendors can leverage this profile to
   issue and consume access tokens in an interoperable manner.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc9068.

Copyright Notice

   Copyright (c) 2021 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
   (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
     1.1.  Requirements Notation and Conventions
     1.2.  Terminology
   2.  JWT Access Token Header and Data Structure
     2.1.  Header
     2.2.  Data Structure
       2.2.1.  Authentication Information Claims
       2.2.2.  Identity Claims
       2.2.3.  Authorization Claims
         2.2.3.1.  Claims for Authorization Outside of Delegation
                 Scenarios
   3.  Requesting a JWT Access Token
   4.  Validating JWT Access Tokens
   5.  Security Considerations
   6.  Privacy Considerations
   7.  IANA Considerations
     7.1.  Media Type Registration
       7.1.1.  Registry Content
     7.2.  Claims Registration
       7.2.1.  Registry Content
         7.2.1.1.  Roles
         7.2.1.2.  Groups
         7.2.1.3.  Entitlements
   8.  References
     8.1.  Normative References
     8.2.  Informative References
   Acknowledgements
   Author's Address

1.  Introduction

   The original OAuth 2.0 Authorization Framework [RFC6749]
   specification does not mandate any specific format for access tokens.
   While that remains perfectly appropriate for many important
   scenarios, in-market use has shown that many commercial OAuth 2.0
   implementations elected to issue access tokens using a format that
   can be parsed and validated by resource servers directly, without
   further authorization server involvement.  The approach is
   particularly common in topologies where the authorization server and
   resource server are not co-located, are not run by the same entity,
   or are otherwise separated by some boundary.  At the time of writing,
   many commercial implementations leverage the JSON Web Token (JWT)
   [RFC7519] format.

   Many vendor-specific JWT access tokens share the same functional
   layout, using JWT claims to convey the information needed to support
   a common set of use cases: token validation, transporting
   authorization information in the form of scopes and entitlements,
   carrying identity information about the subject, and so on.  The
   differences are mostly confined to the claim names and syntax used to
   represent the same entities, suggesting that interoperability could
   be easily achieved by standardizing a common set of claims and
   validation rules.

   The assumption that access tokens are associated with specific
   information doesn't appear only in commercial implementations.
   Various specifications in the OAuth 2.0 family (such as resource
   indicators [RFC8707], OAuth 2.0 bearer token usage [RFC6750], and
   others) postulate the presence of scoping mechanisms, such as an
   audience, in access tokens.  The family of specifications associated
   with introspection also indirectly suggests a fundamental set of
   information that access tokens are expected to carry or at least be
   associated with.

   This specification aims to provide a standardized and interoperable
   profile as an alternative to the proprietary JWT access token layouts
   going forward.  Besides defining a common set of mandatory and
   optional claims, the profile provides clear indications on how
   authorization request parameters determine the content of the issued
   JWT access token, how an authorization server can publish metadata
   relevant to the JWT access tokens it issues, and how a resource
   server should validate incoming JWT access tokens.

   Finally, this specification provides security and privacy
   considerations meant to prevent common mistakes and anti-patterns
   that are likely to occur in naive use of the JWT format to represent
   access tokens.

      Please note: Although both this document and [RFC7523] use JSON
      Web Tokens in the context of the OAuth2 framework, the two
      specifications differ in both intent and mechanics.  Whereas
      [RFC7523] defines how a JWT Bearer Token can be used to request an
      access token, this document describes how to encode access tokens
      in JWT format.

1.1.  Requirements Notation and 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.

1.2.  Terminology

   JWT access token:  An OAuth 2.0 access token encoded in JWT format
      and complying with the requirements described in this
      specification.

   This specification uses the terms "access token", "refresh token",
   "authorization server", "resource server", "authorization endpoint",
   "authorization request", "authorization response", "token endpoint",
   "grant type", "access token request", "access token response", and
   "client" defined by The OAuth 2.0 Authorization Framework [RFC6749].

2.  JWT Access Token Header and Data Structure

2.1.  Header

   JWT access tokens MUST be signed.  Although JWT access tokens can use
   any signing algorithm, use of asymmetric cryptography is RECOMMENDED
   as it simplifies the process of acquiring validation information for
   resource servers (see Section 4).  JWT access tokens MUST NOT use
   "none" as the signing algorithm.  See Section 4 for more details.

   Authorization servers and resource servers conforming to this
   specification MUST include RS256 (as defined in [RFC7518]) among
   their supported signature algorithms.

   This specification registers the "application/at+jwt" media type,
   which can be used to indicate that the content is a JWT access token.
   JWT access tokens MUST include this media type in the "typ" header
   parameter to explicitly declare that the JWT represents an access
   token complying with this profile.  Per the definition of "typ" in
   Section 4.1.9 of [RFC7515], it is RECOMMENDED that the "application/"
   prefix be omitted.  Therefore, the "typ" value used SHOULD be
   "at+jwt".  See the Security Considerations section for details on the
   importance of preventing OpenID Connect ID Tokens (as defined by
   Section 2 of [OpenID.Core]) from being accepted as access tokens by
   resource servers implementing this profile.

2.2.  Data Structure

   The following claims are used in the JWT access token data structure.

   iss  REQUIRED - as defined in Section 4.1.1 of [RFC7519].

   exp  REQUIRED - as defined in Section 4.1.4 of [RFC7519].

   aud  REQUIRED - as defined in Section 4.1.3 of [RFC7519].  See
      Section 3 for indications on how an authorization server should
      determine the value of "aud" depending on the request.

   sub  REQUIRED - as defined in Section 4.1.2 of [RFC7519].  In cases
      of access tokens obtained through grants where a resource owner is
      involved, such as the authorization code grant, the value of "sub"
      SHOULD correspond to the subject identifier of the resource owner.
      In cases of access tokens obtained through grants where no
      resource owner is involved, such as the client credentials grant,
      the value of "sub" SHOULD correspond to an identifier the
      authorization server uses to indicate the client application.  See
      Section 5 for more details on this scenario.  Also, see Section 6
      for a discussion about how different choices in assigning "sub"
      values can impact privacy.

   client_id  REQUIRED - as defined in Section 4.3 of [RFC8693].

   iat  REQUIRED - as defined in Section 4.1.6 of [RFC7519].  This claim
      identifies the time at which the JWT access token was issued.

   jti  REQUIRED - as defined in Section 4.1.7 of [RFC7519].

2.2.1.  Authentication Information Claims

   The claims listed in this section MAY be issued in the context of
   authorization grants involving the resource owner and reflect the
   types and strength of authentication in the access token that the
   authentication server enforced prior to returning the authorization
   response to the client.  Their values are fixed and remain the same
   across all access tokens that derive from a given authorization
   response, whether the access token was obtained directly in the
   response (e.g., via the implicit flow) or after one or more token
   exchanges (e.g., obtaining a fresh access token using a refresh token
   or exchanging one access token for another via [RFC8693] procedures).

   auth_time  OPTIONAL - as defined in Section 2 of [OpenID.Core].

   acr  OPTIONAL - as defined in Section 2 of [OpenID.Core].

   amr  OPTIONAL - as defined in Section 2 of [OpenID.Core].

2.2.2.  Identity Claims

   In the context of authorization grants involving the resource owner,
   commercial authorization servers will often include resource owner
   attributes directly in access tokens so that resource servers can
   consume them directly for authorization or other purposes without any
   further round trips to introspection ([RFC7662]) or UserInfo
   ([OpenID.Core]) endpoints.  This is particularly common in scenarios
   where the client and the resource server belong to the same entity
   and are part of the same solution, as is the case for first-party
   clients invoking their own backend API.

   This profile does not introduce any mechanism for a client to
   directly request the presence of specific claims in JWT access
   tokens, as the authorization server can determine what additional
   claims are required by a particular resource server by taking the
   client_id of the client and the "scope" and the "resource" parameters
   included in the request into consideration.

   Any additional identity attribute whose semantic is well described by
   an entry in the "JSON Web Token (JWT)" IANA registry introduced in
   [RFC7519] SHOULD be encoded using the corresponding claim name, if
   that attribute is to be included in the JWT access token.  Note that
   the JWT IANA registry includes the claims found in Section 5.1 of
   [OpenID.Core].

   Authorization servers MAY return arbitrary attributes not defined in
   any existing specification, as long as the corresponding claim names
   are collision resistant or the access tokens are meant to be used
   only within a private subsystem.  Please refer to Sections 4.2 and
   4.3 of [RFC7519] for details.

   Authorization servers including resource owner attributes in JWT
   access tokens need to exercise care and verify that all privacy
   requirements are met, as discussed in Section 6.

2.2.3.  Authorization Claims

   If an authorization request includes a scope parameter, the
   corresponding issued JWT access token SHOULD include a "scope" claim
   as defined in Section 4.2 of [RFC8693].

   All the individual scope strings in the "scope" claim MUST have
   meaning for the resources indicated in the "aud" claim.  See
   Section 5 for more considerations about the relationship between
   scope strings and resources indicated by the "aud" claim.

2.2.3.1.  Claims for Authorization Outside of Delegation Scenarios

   Many authorization servers embed authorization attributes that go
   beyond the delegated scenarios described by [RFC7519] in the access
   tokens they issue.  Typical examples include resource owner
   memberships in roles and groups that are relevant to the resource
   being accessed, entitlements assigned to the resource owner for the
   targeted resource that the authorization server knows about, and so
   on.

   An authorization server wanting to include such attributes in a JWT
   access token SHOULD use the "groups", "roles", and "entitlements"
   attributes of the "User" resource schema defined by Section 4.1.2 of
   [RFC7643]) as claim types.

   Authorization servers SHOULD encode the corresponding claim values
   according to the guidance defined in [RFC7643].  In particular, a
   non-normative example of a "groups" attribute can be found in
   Section 8.2 of [RFC7643].  No specific vocabulary is provided for
   "roles" and "entitlements".

   Section 7.2.1 of this document provides entries for registering
   "groups", "roles", and "entitlements" attributes from [RFC7643] as
   claim types to be used in this profile.

3.  Requesting a JWT Access Token

   An authorization server can issue a JWT access token in response to
   any authorization grant defined by [RFC6749] and subsequent
   extensions meant to result in an access token.

   If the request includes a "resource" parameter (as defined in
   [RFC8707]), the resulting JWT access token "aud" claim SHOULD have
   the same value as the "resource" parameter in the request.

   Example request below:

   GET /as/authorization.oauth2?response_type=code
           &client_id=s6BhdRkqt3
           &state=xyz
           &scope=openid%20profile%20reademail
           &redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb
           &resource=https%3A%2F%2Frs.example.com%2F HTTP/1.1
        Host: authorization-server.example.com

     Figure 1: Authorization Request with Resource and Scope Parameters

   Once redeemed, the code obtained from the request above will result
   in a JWT access token in the form shown below:

   Header:

      {"typ":"at+JWT","alg":"RS256","kid":"RjEwOwOA"}

   Claims:

      {
        "iss": "https://authorization-server.example.com/",
        "sub": "5ba552d67",
        "aud":   "https://rs.example.com/",
        "exp": 1639528912,
        "iat": 1618354090,
        "jti" : "dbe39bf3a3ba4238a513f51d6e1691c4",
        "client_id": "s6BhdRkqt3",
        "scope": "openid profile reademail"
      }

       Figure 2: The Header and JWT Claims Set of a JWT Access Token

   The authorization server MUST NOT issue a JWT access token if the
   authorization granted by the token would be ambiguous.  See Section 5
   for more details about common cases that might lead to ambiguity and
   strategies an authorization server can enact to prevent them.

   If the request does not include a "resource" parameter, the
   authorization server MUST use a default resource indicator in the
   "aud" claim.  If a "scope" parameter is present in the request, the
   authorization server SHOULD use it to infer the value of the default
   resource indicator to be used in the "aud" claim.  The mechanism
   through which scopes are associated with default resource indicator
   values is outside the scope of this specification.  If the values in
   the "scope" parameter refer to different default resource indicator
   values, the authorization server SHOULD reject the request with
   "invalid_scope" as described in Section 4.1.2.1 of [RFC6749].

4.  Validating JWT Access Tokens

   For the purpose of facilitating validation data retrieval, it is
   RECOMMENDED here that authorization servers sign JWT access tokens
   with an asymmetric algorithm.

   Authorization servers SHOULD use OAuth 2.0 Authorization Server
   Metadata [RFC8414] to advertise to resource servers their signing
   keys via "jwks_uri" and what "iss" claim value to expect via the
   "issuer" metadata value.  Alternatively, authorization servers
   implementing OpenID Connect MAY use the OpenID Connect discovery
   [OpenID.Discovery] document for the same purpose.  If an
   authorization server supports both OAuth 2.0 Authorization Server
   Metadata and OpenID Connect discovery, the values provided MUST be
   consistent across the two publication methods.

   An authorization server MAY elect to use different keys to sign
   OpenID Connect ID Tokens and JWT access tokens.  This specification
   does not provide a mechanism for identifying a specific key as the
   one used to sign JWT access tokens.  An authorization server can sign
   JWT access tokens with any of the keys advertised via authorization
   server (AS) metadata or OpenID Connect discovery.  See Section 5 for
   further guidance on security implications.

   Resource servers receiving a JWT access token MUST validate it in the
   following manner.

   *  The resource server MUST verify that the "typ" header value is
      "at+jwt" or "application/at+jwt" and reject tokens carrying any
      other value.

   *  If the JWT access token is encrypted, decrypt it using the keys
      and algorithms that the resource server specified during
      registration.  If encryption was negotiated with the authorization
      server at registration time and the incoming JWT access token is
      not encrypted, the resource server SHOULD reject it.

   *  The issuer identifier for the authorization server (which is
      typically obtained during discovery) MUST exactly match the value
      of the "iss" claim.

   *  The resource server MUST validate that the "aud" claim contains a
      resource indicator value corresponding to an identifier the
      resource server expects for itself.  The JWT access token MUST be
      rejected if "aud" does not contain a resource indicator of the
      current resource server as a valid audience.

   *  The resource server MUST validate the signature of all incoming
      JWT access tokens according to [RFC7515] using the algorithm
      specified in the JWT "alg" Header Parameter.  The resource server
      MUST reject any JWT in which the value of "alg" is "none".  The
      resource server MUST use the keys provided by the authorization
      server.

   *  The current time MUST be before the time represented by the "exp"
      claim.  Implementers MAY provide for some small leeway, usually no
      more than a few minutes, to account for clock skew.

   The resource server MUST handle errors as described in Section 3.1 of
   [RFC6750].  In particular, in case of any failure in the validation
   checks listed above, the authorization server response MUST include
   the error code "invalid_token".  Please note that this requirement
   does not prevent JWT access tokens from using authentication schemes
   other than "Bearer".

   If the JWT access token includes authorization claims as described in
   Section 2.2.3, the resource server SHOULD use them in combination
   with any other contextual information available to determine whether
   the current call should be authorized or rejected.  Details about how
   a resource server performs those checks is beyond the scope of this
   profile specification.

5.  Security Considerations

   The JWT access token data layout described here is very similar to
   that of the id_token as defined by [OpenID.Core].  The explicit
   typing required in this profile, in line with the recommendations in
   [RFC8725], helps the resource server to distinguish between JWT
   access tokens and OpenID Connect ID Tokens.

   Authorization servers should prevent scenarios where clients can
   affect the value of the "sub" claim in ways that could confuse
   resource servers.  For example, if the authorization server elects to
   use the client_id as the "sub" value for access tokens issued using
   the client credentials grant, the authorization server should prevent
   clients from registering an arbitrary client_id value, as this would
   allow malicious clients to select the sub of a high-privilege
   resource owner and confuse any authorization logic on the resource
   server relying on the "sub" value.  For more details, please refer to
   Section 4.14 of [OAuth2.Security.BestPractices].

   To prevent cross-JWT confusion, authorization servers MUST use a
   distinct identifier as an "aud" claim value to uniquely identify
   access tokens issued by the same issuer for distinct resources.  For
   more details on cross-JWT confusion, please refer to Section 2.8 of
   [RFC8725].

   Authorization servers should use particular care when handling
   requests that might lead to ambiguous authorization grants.  For
   example, if a request includes multiple resource indicators, the
   authorization server should ensure that each scope string included in
   the resulting JWT access token, if any, can be unambiguously
   correlated to a specific resource among the ones listed in the "aud"
   claim.  The details on how to recognize and mitigate this and other
   ambiguous situations is highly scenario dependent and hence is out of
   scope for this profile.

   Authorization servers cannot rely on the use of different keys for
   signing OpenID Connect ID Tokens and JWT tokens as a method to
   safeguard against the consequences of leaking specific keys.  Given
   that resource servers have no way of knowing what key should be used
   to validate JWT access tokens in particular, they have to accept
   signatures performed with any of the keys published in AS metadata or
   OpenID Connect discovery; consequently, an attacker just needs to
   compromise any key among the ones published to be able to generate
   and sign JWTs that will be accepted as valid by the resource server.

6.  Privacy Considerations

   As JWT access tokens carry information by value, it now becomes
   possible for clients and potentially even end users to directly peek
   inside the token claims collection of unencrypted tokens.

   The client MUST NOT inspect the content of the access token: the
   authorization server and the resource server might decide to change
   the token format at any time (for example, by switching from this
   profile to opaque tokens); hence, any logic in the client relying on
   the ability to read the access token content would break without
   recourse.  The OAuth 2.0 framework assumes that access tokens are
   treated as opaque by clients.  Administrators of authorization
   servers should also take into account that the content of an access
   token is visible to the client.  Whenever client access to the access
   token content presents privacy issues for a given scenario, the
   authorization server needs to take explicit steps to prevent them.

   In scenarios in which JWT access tokens are accessible to the end
   user, it should be evaluated whether the information can be accessed
   without privacy violations (for example, if an end user would simply
   access his or her own personal information) or if steps must be taken
   to enforce confidentiality.

   Possible measures to prevent leakage of information to clients and
   end users include: encrypting the access token, encrypting the
   sensitive claims, omitting the sensitive claims or not using this
   profile, and falling back on opaque access tokens.

   In every scenario, the content of the JWT access token will
   eventually be accessible to the resource server.  It's important to
   evaluate whether the resource server gained the proper entitlement to
   have access to any content received in the form of claims, for
   example, through user consent in some form, policies and agreements
   with the organization running the authorization servers, and so on.
   For example, a user might not wish to consent to granting given
   resource server information about any of the non-mandatory claims
   enumerated in Section 2 (and its subsections).

   This profile mandates the presence of the "sub" claim in every JWT
   access token, making it possible for resource servers to rely on that
   information for correlating incoming requests with data stored
   locally for the authenticated principal.  Although the ability to
   correlate requests might be required by design in many scenarios,
   there are scenarios where the authorization server might want to
   prevent correlation.  The "sub" claim should be populated by the
   authorization servers according to a privacy impact assessment.  For
   instance, if a solution requires preventing tracking of principal
   activities across multiple resource servers, the authorization server
   should ensure that JWT access tokens meant for different resource
   servers have distinct "sub" values that cannot be correlated in the
   event of resource server collusion.  Similarly, if a solution
   requires preventing a resource server from correlating the
   principal's activity within the resource itself, the authorization
   server should assign different "sub" values for every JWT access
   token issued.  In turn, the client should obtain a new JWT access
   token for every call to the resource server to ensure that the
   resource server receives different "sub" and "jti" values at every
   call, thus preventing correlation between distinct requests.

7.  IANA Considerations

7.1.  Media Type Registration

7.1.1.  Registry Content

   This section registers "application/at+jwt", a new media type
   [RFC2046] in the "Media Types" registry [IANA.MediaTypes] in the
   manner described in [RFC6838].  It can be used to indicate that the
   content is an access token encoded in JWT format.

   Type name:  Application

   Subtype name:  at+jwt

   Required parameters:  N/A

   Optional parameters:  N/A

   Encoding considerations:  Binary; JWT values are encoded as a series
      of base64url-encoded values (with trailing '=' characters
      removed), some of which may be the empty string, separated by
      period ('.') characters.

   Security considerations:  See the Security Considerations section of
      RFC 9068.

   Interoperability considerations:  N/A

   Published specification:  RFC 9068

   Applications that use this media type:  Applications that access
      resource servers using OAuth 2.0 access tokens encoded in JWT
      format

   Fragment identifier considerations:  N/A

   Additional information:

      Magic number(s):  N/A
      File extension(s):  N/A
      Macintosh file type code(s):  N/A

   Person & email address to contact for further information:
      Vittorio Bertocci <vittorio@auth0.com>

   Intended usage:  COMMON

   Restrictions on usage:  None

   Author:  Vittorio Bertocci <vittorio@auth0.com>

   Change controller:  IETF

   Provisional registration?  No

7.2.  Claims Registration

   Section 2.2.3.1 of this specification refers to the attributes
   "roles", "groups", "entitlements" defined in [RFC7643] to express
   authorization information in JWT access tokens.  This section
   registers those attributes as claims in the "JSON Web Token (JWT)"
   IANA registry introduced in [RFC7519].

7.2.1.  Registry Content

7.2.1.1.  Roles

   Claim Name:  roles
   Claim Description:  Roles
   Change Controller:  IETF
   Specification Document(s):  Section 4.1.2 of [RFC7643] and
      Section 2.2.3.1 of RFC 9068

7.2.1.2.  Groups

   Claim Name:  groups
   Claim Description:  Groups
   Change Controller:  IETF
   Specification Document(s):  Section 4.1.2 of [RFC7643] and
      Section 2.2.3.1 of RFC 9068

7.2.1.3.  Entitlements

   Claim Name:  entitlements
   Claim Description:  Entitlements
   Change Controller:  IETF
   Specification Document(s):  Section 4.1.2 of [RFC7643] and
      Section 2.2.3.1 of RFC 9068

8.  References

8.1.  Normative References

   [OpenID.Core]
              Sakimura, N., Bradley, J., Jones, M., de Medeiros, B., and
              C. Mortimore, "OpenID Connect Core 1.0 incorporating
              errata set 1", November 2014,
              <https://openid.net/specs/openid-connect-core-1_0.html>.

   [OpenID.Discovery]
              Sakimura, N., Bradley, J., Jones, M., and E. Jay, "OpenID
              Connect Discovery 1.0 incorporating errata set 1",
              November 2014, <https://openid.net/specs/openid-connect-
              discovery-1_0.html>.

   [RFC2046]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part Two: Media Types", RFC 2046,
              DOI 10.17487/RFC2046, November 1996,
              <https://www.rfc-editor.org/info/rfc2046>.

   [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>.

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

   [RFC6838]  Freed, N., Klensin, J., and T. Hansen, "Media Type
              Specifications and Registration Procedures", BCP 13,
              RFC 6838, DOI 10.17487/RFC6838, January 2013,
              <https://www.rfc-editor.org/info/rfc6838>.

   [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>.

   [RFC7518]  Jones, M., "JSON Web Algorithms (JWA)", RFC 7518,
              DOI 10.17487/RFC7518, May 2015,
              <https://www.rfc-editor.org/info/rfc7518>.

   [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>.

   [RFC7643]  Hunt, P., Ed., Grizzle, K., Wahlstroem, E., and C.
              Mortimore, "System for Cross-domain Identity Management:
              Core Schema", RFC 7643, DOI 10.17487/RFC7643, September
              2015, <https://www.rfc-editor.org/info/rfc7643>.

   [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>.

   [RFC8414]  Jones, M., Sakimura, N., and J. Bradley, "OAuth 2.0
              Authorization Server Metadata", RFC 8414,
              DOI 10.17487/RFC8414, June 2018,
              <https://www.rfc-editor.org/info/rfc8414>.

   [RFC8693]  Jones, M., Nadalin, A., Campbell, B., Ed., Bradley, J.,
              and C. Mortimore, "OAuth 2.0 Token Exchange", RFC 8693,
              DOI 10.17487/RFC8693, January 2020,
              <https://www.rfc-editor.org/info/rfc8693>.

   [RFC8707]  Campbell, B., Bradley, J., and H. Tschofenig, "Resource
              Indicators for OAuth 2.0", RFC 8707, DOI 10.17487/RFC8707,
              February 2020, <https://www.rfc-editor.org/info/rfc8707>.

   [RFC8725]  Sheffer, Y., Hardt, D., and M. Jones, "JSON Web Token Best
              Current Practices", BCP 225, RFC 8725,
              DOI 10.17487/RFC8725, February 2020,
              <https://www.rfc-editor.org/info/rfc8725>.

8.2.  Informative References

   [IANA.MediaTypes]
              IANA, "Media Types",
              <https://www.iana.org/assignments/media-types/>.

   [OAuth2.Security.BestPractices]
              Lodderstedt, T., Bradley, J., Labunets, A., and D. Fett,
              "OAuth 2.0 Security Best Current Practice", Work in
              Progress, Internet-Draft, draft-ietf-oauth-security-
              topics-18, 13 April 2021,
              <https://datatracker.ietf.org/doc/html/draft-ietf-oauth-
              security-topics-18>.

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

   [RFC7523]  Jones, M., Campbell, B., and C. Mortimore, "JSON Web Token
              (JWT) Profile for OAuth 2.0 Client Authentication and
              Authorization Grants", RFC 7523, DOI 10.17487/RFC7523, May
              2015, <https://www.rfc-editor.org/info/rfc7523>.

   [RFC7662]  Richer, J., Ed., "OAuth 2.0 Token Introspection",
              RFC 7662, DOI 10.17487/RFC7662, October 2015,
              <https://www.rfc-editor.org/info/rfc7662>.

Acknowledgements

   The initial set of requirements informing this specification was
   extracted by numerous examples of access tokens issued in JWT format
   by production systems.  Thanks to Dominick Baier (IdentityServer),
   Brian Campbell (Ping Identity), Daniel Dobalian (Microsoft), and Karl
   Guinness (Okta) for providing sample tokens issued by their products
   and services.  Brian Campbell and Filip Skokan provided early
   feedback that shaped the direction of the specification.  This
   profile was discussed at length during the OAuth Security Workshop
   2019, with several individuals contributing ideas and feedback.  The
   author would like to acknowledge the contributions of:

   John Bradley, Brian Campbell, Vladimir Dzhuvinov, Torsten
   Lodderstedt, Nat Sakimura, Hannes Tschofenig, and everyone who
   actively participated in the unconference discussions.

   The following individuals contributed useful feedback and insights on
   the drafts, both at the IETF OAuth 2.0 WG mailing list and during the
   28th Internet Identity Workshop (IIW 28):

   Dale Olds, George Fletcher, David Waite, Michael Engan, Mike Jones,
   Hans Zandbelt, Vladimir Dzhuvinov, Martin Schanzenbach, Aaron
   Parecki, Annabelle Richard Backman, Dick Hardt, Denis Pinkas,
   Benjamin Kaduk, Dominick Baier, Andrii Deinega, Mike Jones, and
   everyone who actively participated in the IIW 28 unconference
   discussions and the IETF OAuth 2.0 WG mailing list discussions.
   Thanks to Roman Danyliw for the AD review; Joseph Salowey and Roni
   Even for the SECDIR and GENART reviews; and Francesca Palomini, Lars
   Eggert, Murray Kucherawy, Roberto Polli, Martin Duke, Benjamin Kaduk
   for the IESG reviews.

Author's Address

   Vittorio Bertocci
   Auth0

   Email: vittorio@auth0.com
