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rfc:rfc8414

Internet Engineering Task Force (IETF) M. Jones Request for Comments: 8414 Microsoft Category: Standards Track N. Sakimura ISSN: 2070-1721 NRI

                                                            J. Bradley
                                                                Yubico
                                                             June 2018
              OAuth 2.0 Authorization Server Metadata

Abstract

 This specification defines a metadata format that an OAuth 2.0 client
 can use to obtain the information needed to interact with an
 OAuth 2.0 authorization server, including its endpoint locations and
 authorization server capabilities.

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/rfc8414.

Copyright Notice

 Copyright (c) 2018 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.

Jones, et al. Standards Track [Page 1] RFC 8414 OAuth 2.0 Authorization Server Metadata June 2018

Table of Contents

 1. Introduction ....................................................2
    1.1. Requirements Notation and Conventions ......................3
    1.2. Terminology ................................................3
 2. Authorization Server Metadata ...................................4
    2.1. Signed Authorization Server Metadata .......................8
 3. Obtaining Authorization Server Metadata .........................8
    3.1. Authorization Server Metadata Request ......................9
    3.2. Authorization Server Metadata Response ....................10
    3.3. Authorization Server Metadata Validation ..................11
 4. String Operations ..............................................11
 5. Compatibility Notes ............................................11
 6. Security Considerations ........................................12
    6.1. TLS Requirements ..........................................12
    6.2. Impersonation Attacks .....................................12
    6.3. Publishing Metadata in a Standard Format ..................13
    6.4. Protected Resources .......................................13
 7. IANA Considerations ............................................14
    7.1. OAuth Authorization Server Metadata Registry ..............14
         7.1.1. Registration Template ..............................15
         7.1.2. Initial Registry Contents ..........................16
    7.2. Updated Registration Instructions .........................19
    7.3. Well-Known URI Registry ...................................19
         7.3.1. Registry Contents ..................................19
 8. References .....................................................20
    8.1. Normative References ......................................20
    8.2. Informative References ....................................22
 Acknowledgements ..................................................23
 Authors' Addresses ................................................23

1. Introduction

 This specification generalizes the metadata format defined by "OpenID
 Connect Discovery 1.0" [OpenID.Discovery] in a way that is compatible
 with OpenID Connect Discovery while being applicable to a wider set
 of OAuth 2.0 use cases.  This is intentionally parallel to the way
 that "OAuth 2.0 Dynamic Client Registration Protocol" [RFC7591]
 generalized the dynamic client registration mechanisms defined by
 "OpenID Connect Dynamic Client Registration 1.0"
 [OpenID.Registration] in a way that is compatible with it.
 The metadata for an authorization server is retrieved from a well-
 known location as a JSON [RFC8259] document, which declares its
 endpoint locations and authorization server capabilities.  This
 process is described in Section 3.

Jones, et al. Standards Track [Page 2] RFC 8414 OAuth 2.0 Authorization Server Metadata June 2018

 This metadata can be communicated either in a self-asserted fashion
 by the server origin via HTTPS or as a set of signed metadata values
 represented as claims in a JSON Web Token (JWT) [JWT].  In the JWT
 case, the issuer is vouching for the validity of the data about the
 authorization server.  This is analogous to the role that the
 Software Statement plays in OAuth Dynamic Client Registration
 [RFC7591].
 The means by which the client chooses an authorization server is out
 of scope.  In some cases, its issuer identifier may be manually
 configured into the client.  In other cases, it may be dynamically
 discovered, for instance, through the use of WebFinger [RFC7033], as
 described in Section 2 of "OpenID Connect Discovery 1.0"
 [OpenID.Discovery].

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.
 All uses of JSON Web Signature (JWS) [JWS] and JSON Web Encryption
 (JWE) [JWE] data structures in this specification utilize the JWS
 Compact Serialization or the JWE Compact Serialization; the JWS JSON
 Serialization and the JWE JSON Serialization are not used.

1.2. Terminology

 This specification uses the terms "Access Token", "Authorization
 Code", "Authorization Endpoint", "Authorization Grant",
 "Authorization Server", "Client", "Client Authentication", "Client
 Identifier", "Client Secret", "Grant Type", "Protected Resource",
 "Redirection URI", "Refresh Token", "Resource Owner", "Resource
 Server", "Response Type", and "Token Endpoint" defined by OAuth 2.0
 [RFC6749]; the terms "Claim Name", "Claim Value", and "JSON Web Token
 (JWT)" defined by JSON Web Token (JWT) [JWT]; and the term "Response
 Mode" defined by "OAuth 2.0 Multiple Response Type Encoding
 Practices" [OAuth.Responses].

Jones, et al. Standards Track [Page 3] RFC 8414 OAuth 2.0 Authorization Server Metadata June 2018

2. Authorization Server Metadata

 Authorization servers can have metadata describing their
 configuration.  The following authorization server metadata values
 are used by this specification and are registered in the IANA "OAuth
 Authorization Server Metadata" registry established in Section 7.1:
 issuer
    REQUIRED.  The authorization server's issuer identifier, which is
    a URL that uses the "https" scheme and has no query or fragment
    components.  Authorization server metadata is published at a
    location that is ".well-known" according to RFC 5785 [RFC5785]
    derived from this issuer identifier, as described in Section 3.
    The issuer identifier is used to prevent authorization server mix-
    up attacks, as described in "OAuth 2.0 Mix-Up Mitigation"
    [MIX-UP].
 authorization_endpoint
    URL of the authorization server's authorization endpoint
    [RFC6749].  This is REQUIRED unless no grant types are supported
    that use the authorization endpoint.
 token_endpoint
    URL of the authorization server's token endpoint [RFC6749].  This
    is REQUIRED unless only the implicit grant type is supported.
 jwks_uri
    OPTIONAL.  URL of the authorization server's JWK Set [JWK]
    document.  The referenced document contains the signing key(s) the
    client uses to validate signatures from the authorization server.
    This URL MUST use the "https" scheme.  The JWK Set MAY also
    contain the server's encryption key or keys, which are used by
    clients to encrypt requests to the server.  When both signing and
    encryption keys are made available, a "use" (public key use)
    parameter value is REQUIRED for all keys in the referenced JWK Set
    to indicate each key's intended usage.
 registration_endpoint
    OPTIONAL.  URL of the authorization server's OAuth 2.0 Dynamic
    Client Registration endpoint [RFC7591].
 scopes_supported
    RECOMMENDED.  JSON array containing a list of the OAuth 2.0
    [RFC6749] "scope" values that this authorization server supports.
    Servers MAY choose not to advertise some supported scope values
    even when this parameter is used.

Jones, et al. Standards Track [Page 4] RFC 8414 OAuth 2.0 Authorization Server Metadata June 2018

 response_types_supported
    REQUIRED.  JSON array containing a list of the OAuth 2.0
    "response_type" values that this authorization server supports.
    The array values used are the same as those used with the
    "response_types" parameter defined by "OAuth 2.0 Dynamic Client
    Registration Protocol" [RFC7591].
 response_modes_supported
    OPTIONAL.  JSON array containing a list of the OAuth 2.0
    "response_mode" values that this authorization server supports, as
    specified in "OAuth 2.0 Multiple Response Type Encoding Practices"
    [OAuth.Responses].  If omitted, the default is "["query",
    "fragment"]".  The response mode value "form_post" is also defined
    in "OAuth 2.0 Form Post Response Mode" [OAuth.Post].
 grant_types_supported
    OPTIONAL.  JSON array containing a list of the OAuth 2.0 grant
    type values that this authorization server supports.  The array
    values used are the same as those used with the "grant_types"
    parameter defined by "OAuth 2.0 Dynamic Client Registration
    Protocol" [RFC7591].  If omitted, the default value is
    "["authorization_code", "implicit"]".
 token_endpoint_auth_methods_supported
    OPTIONAL.  JSON array containing a list of client authentication
    methods supported by this token endpoint.  Client authentication
    method values are used in the "token_endpoint_auth_method"
    parameter defined in Section 2 of [RFC7591].  If omitted, the
    default is "client_secret_basic" -- the HTTP Basic Authentication
    Scheme specified in Section 2.3.1 of OAuth 2.0 [RFC6749].
 token_endpoint_auth_signing_alg_values_supported
    OPTIONAL.  JSON array containing a list of the JWS signing
    algorithms ("alg" values) supported by the token endpoint for the
    signature on the JWT [JWT] used to authenticate the client at the
    token endpoint for the "private_key_jwt" and "client_secret_jwt"
    authentication methods.  This metadata entry MUST be present if
    either of these authentication methods are specified in the
    "token_endpoint_auth_methods_supported" entry.  No default
    algorithms are implied if this entry is omitted.  Servers SHOULD
    support "RS256".  The value "none" MUST NOT be used.
 service_documentation
    OPTIONAL.  URL of a page containing human-readable information
    that developers might want or need to know when using the
    authorization server.  In particular, if the authorization server

Jones, et al. Standards Track [Page 5] RFC 8414 OAuth 2.0 Authorization Server Metadata June 2018

    does not support Dynamic Client Registration, then information on
    how to register clients needs to be provided in this
    documentation.
 ui_locales_supported
    OPTIONAL.  Languages and scripts supported for the user interface,
    represented as a JSON array of language tag values from BCP 47
    [RFC5646].  If omitted, the set of supported languages and scripts
    is unspecified.
 op_policy_uri
    OPTIONAL.  URL that the authorization server provides to the
    person registering the client to read about the authorization
    server's requirements on how the client can use the data provided
    by the authorization server.  The registration process SHOULD
    display this URL to the person registering the client if it is
    given.  As described in Section 5, despite the identifier
    "op_policy_uri" appearing to be OpenID-specific, its usage in this
    specification is actually referring to a general OAuth 2.0 feature
    that is not specific to OpenID Connect.
 op_tos_uri
    OPTIONAL.  URL that the authorization server provides to the
    person registering the client to read about the authorization
    server's terms of service.  The registration process SHOULD
    display this URL to the person registering the client if it is
    given.  As described in Section 5, despite the identifier
    "op_tos_uri", appearing to be OpenID-specific, its usage in this
    specification is actually referring to a general OAuth 2.0 feature
    that is not specific to OpenID Connect.
 revocation_endpoint
    OPTIONAL.  URL of the authorization server's OAuth 2.0 revocation
    endpoint [RFC7009].
 revocation_endpoint_auth_methods_supported
    OPTIONAL.  JSON array containing a list of client authentication
    methods supported by this revocation endpoint.  The valid client
    authentication method values are those registered in the IANA
    "OAuth Token Endpoint Authentication Methods" registry
    [IANA.OAuth.Parameters].  If omitted, the default is
    "client_secret_basic" -- the HTTP Basic Authentication Scheme
    specified in Section 2.3.1 of OAuth 2.0 [RFC6749].
 revocation_endpoint_auth_signing_alg_values_supported
    OPTIONAL.  JSON array containing a list of the JWS signing
    algorithms ("alg" values) supported by the revocation endpoint for
    the signature on the JWT [JWT] used to authenticate the client at

Jones, et al. Standards Track [Page 6] RFC 8414 OAuth 2.0 Authorization Server Metadata June 2018

    the revocation endpoint for the "private_key_jwt" and
    "client_secret_jwt" authentication methods.  This metadata entry
    MUST be present if either of these authentication methods are
    specified in the "revocation_endpoint_auth_methods_supported"
    entry.  No default algorithms are implied if this entry is
    omitted.  The value "none" MUST NOT be used.
 introspection_endpoint
    OPTIONAL.  URL of the authorization server's OAuth 2.0
    introspection endpoint [RFC7662].
 introspection_endpoint_auth_methods_supported
    OPTIONAL.  JSON array containing a list of client authentication
    methods supported by this introspection endpoint.  The valid
    client authentication method values are those registered in the
    IANA "OAuth Token Endpoint Authentication Methods" registry
    [IANA.OAuth.Parameters] or those registered in the IANA "OAuth
    Access Token Types" registry [IANA.OAuth.Parameters].  (These
    values are and will remain distinct, due to Section 7.2.)  If
    omitted, the set of supported authentication methods MUST be
    determined by other means.
 introspection_endpoint_auth_signing_alg_values_supported
    OPTIONAL.  JSON array containing a list of the JWS signing
    algorithms ("alg" values) supported by the introspection endpoint
    for the signature on the JWT [JWT] used to authenticate the client
    at the introspection endpoint for the "private_key_jwt" and
    "client_secret_jwt" authentication methods.  This metadata entry
    MUST be present if either of these authentication methods are
    specified in the "introspection_endpoint_auth_methods_supported"
    entry.  No default algorithms are implied if this entry is
    omitted.  The value "none" MUST NOT be used.
 code_challenge_methods_supported
    OPTIONAL.  JSON array containing a list of Proof Key for Code
    Exchange (PKCE) [RFC7636] code challenge methods supported by this
    authorization server.  Code challenge method values are used in
    the "code_challenge_method" parameter defined in Section 4.3 of
    [RFC7636].  The valid code challenge method values are those
    registered in the IANA "PKCE Code Challenge Methods" registry
    [IANA.OAuth.Parameters].  If omitted, the authorization server
    does not support PKCE.
 Additional authorization server metadata parameters MAY also be used.
 Some are defined by other specifications, such as OpenID Connect
 Discovery 1.0 [OpenID.Discovery].

Jones, et al. Standards Track [Page 7] RFC 8414 OAuth 2.0 Authorization Server Metadata June 2018

2.1. Signed Authorization Server Metadata

 In addition to JSON elements, metadata values MAY also be provided as
 a "signed_metadata" value, which is a JSON Web Token (JWT) [JWT] that
 asserts metadata values about the authorization server as a bundle.
 A set of claims that can be used in signed metadata is defined in
 Section 2.  The signed metadata MUST be digitally signed or MACed
 using JSON Web Signature (JWS) [JWS] and MUST contain an "iss"
 (issuer) claim denoting the party attesting to the claims in the
 signed metadata.  Consumers of the metadata MAY ignore the signed
 metadata if they do not support this feature.  If the consumer of the
 metadata supports signed metadata, metadata values conveyed in the
 signed metadata MUST take precedence over the corresponding values
 conveyed using plain JSON elements.
 Signed metadata is included in the authorization server metadata JSON
 object using this OPTIONAL member:
 signed_metadata
    A JWT containing metadata values about the authorization server as
    claims.  This is a string value consisting of the entire signed
    JWT.  A "signed_metadata" metadata value SHOULD NOT appear as a
    claim in the JWT.

3. Obtaining Authorization Server Metadata

 Authorization servers supporting metadata MUST make a JSON document
 containing metadata as specified in Section 2 available at a path
 formed by inserting a well-known URI string into the authorization
 server's issuer identifier between the host component and the path
 component, if any.  By default, the well-known URI string used is
 "/.well-known/oauth-authorization-server".  This path MUST use the
 "https" scheme.  The syntax and semantics of ".well-known" are
 defined in RFC 5785 [RFC5785].  The well-known URI suffix used MUST
 be registered in the IANA "Well-Known URIs" registry
 [IANA.well-known].
 Different applications utilizing OAuth authorization servers in
 application-specific ways may define and register different well-
 known URI suffixes used to publish authorization server metadata as
 used by those applications.  For instance, if the example application
 uses an OAuth authorization server in an example-specific way, and
 there are example-specific metadata values that it needs to publish,
 then it might register and use the "example-configuration" URI suffix
 and publish the metadata document at the path formed by inserting
 "/.well-known/example-configuration" between the host and path
 components of the authorization server's issuer identifier.
 Alternatively, many such applications will use the default well-known

Jones, et al. Standards Track [Page 8] RFC 8414 OAuth 2.0 Authorization Server Metadata June 2018

 URI string "/.well-known/oauth-authorization-server", which is the
 right choice for general-purpose OAuth authorization servers, and not
 register an application-specific one.
 An OAuth 2.0 application using this specification MUST specify what
 well-known URI suffix it will use for this purpose.  The same
 authorization server MAY choose to publish its metadata at multiple
 well-known locations derived from its issuer identifier, for example,
 publishing metadata at both "/.well-known/example-configuration" and
 "/.well-known/oauth-authorization-server".
 Some OAuth applications will choose to use the well-known URI suffix
 "openid-configuration".  As described in Section 5, despite the
 identifier "/.well-known/openid-configuration", appearing to be
 OpenID specific, its usage in this specification is actually
 referring to a general OAuth 2.0 feature that is not specific to
 OpenID Connect.

3.1. Authorization Server Metadata Request

 An authorization server metadata document MUST be queried using an
 HTTP "GET" request at the previously specified path.
 The client would make the following request when the issuer
 identifier is "https://example.com" and the well-known URI suffix is
 "oauth-authorization-server" to obtain the metadata, since the issuer
 identifier contains no path component:
   GET /.well-known/oauth-authorization-server HTTP/1.1
   Host: example.com
 If the issuer identifier value contains a path component, any
 terminating "/" MUST be removed before inserting "/.well-known/" and
 the well-known URI suffix between the host component and the path
 component.  The client would make the following request when the
 issuer identifier is "https://example.com/issuer1" and the well-known
 URI suffix is "oauth-authorization-server" to obtain the metadata,
 since the issuer identifier contains a path component:
   GET /.well-known/oauth-authorization-server/issuer1 HTTP/1.1
   Host: example.com
 Using path components enables supporting multiple issuers per host.
 This is required in some multi-tenant hosting configurations.  This
 use of ".well-known" is for supporting multiple issuers per host;
 unlike its use in RFC 5785 [RFC5785], it does not provide general
 information about the host.

Jones, et al. Standards Track [Page 9] RFC 8414 OAuth 2.0 Authorization Server Metadata June 2018

3.2. Authorization Server Metadata Response

 The response is a set of claims about the authorization server's
 configuration, including all necessary endpoints and public key
 location information.  A successful response MUST use the 200 OK HTTP
 status code and return a JSON object using the "application/json"
 content type that contains a set of claims as its members that are a
 subset of the metadata values defined in Section 2.  Other claims MAY
 also be returned.
 Claims that return multiple values are represented as JSON arrays.
 Claims with zero elements MUST be omitted from the response.
 An error response uses the applicable HTTP status code value.
 The following is a non-normative example response:
   HTTP/1.1 200 OK
   Content-Type: application/json
   {
    "issuer":
      "https://server.example.com",
    "authorization_endpoint":
      "https://server.example.com/authorize",
    "token_endpoint":
      "https://server.example.com/token",
    "token_endpoint_auth_methods_supported":
      ["client_secret_basic", "private_key_jwt"],
    "token_endpoint_auth_signing_alg_values_supported":
      ["RS256", "ES256"],
    "userinfo_endpoint":
      "https://server.example.com/userinfo",
    "jwks_uri":
      "https://server.example.com/jwks.json",
    "registration_endpoint":
      "https://server.example.com/register",
    "scopes_supported":
      ["openid", "profile", "email", "address",
       "phone", "offline_access"],
    "response_types_supported":
      ["code", "code token"],
    "service_documentation":
      "http://server.example.com/service_documentation.html",
    "ui_locales_supported":
      ["en-US", "en-GB", "en-CA", "fr-FR", "fr-CA"]
   }

Jones, et al. Standards Track [Page 10] RFC 8414 OAuth 2.0 Authorization Server Metadata June 2018

3.3. Authorization Server Metadata Validation

 The "issuer" value returned MUST be identical to the authorization
 server's issuer identifier value into which the well-known URI string
 was inserted to create the URL used to retrieve the metadata.  If
 these values are not identical, the data contained in the response
 MUST NOT be used.

4. String Operations

 Processing some OAuth 2.0 messages requires comparing values in the
 messages to known values.  For example, the member names in the
 metadata response might be compared to specific member names such as
 "issuer".  Comparing Unicode [UNICODE] strings, however, has
 significant security implications.
 Therefore, comparisons between JSON strings and other Unicode strings
 MUST be performed as specified below:
 1.  Remove any JSON-applied escaping to produce an array of Unicode
     code points.
 2.  Unicode Normalization [USA15] MUST NOT be applied at any point to
     either the JSON string or the string it is to be compared
     against.
 3.  Comparisons between the two strings MUST be performed as a
     Unicode code-point-to-code-point equality comparison.
 Note that this is the same equality comparison procedure described in
 Section 8.3 of [RFC8259].

5. Compatibility Notes

 The identifiers "/.well-known/openid-configuration", "op_policy_uri",
 and "op_tos_uri" contain strings referring to the OpenID Connect
 [OpenID.Core] family of specifications that were originally defined
 by "OpenID Connect Discovery 1.0" [OpenID.Discovery].  Despite the
 reuse of these identifiers that appear to be OpenID specific, their
 usage in this specification is actually referring to general OAuth
 2.0 features that are not specific to OpenID Connect.
 The algorithm for transforming the issuer identifier to an
 authorization server metadata location defined in Section 3 is
 equivalent to the corresponding transformation defined in Section 4
 of "OpenID Connect Discovery 1.0" [OpenID.Discovery], provided that
 the issuer identifier contains no path component.  However, they are
 different when there is a path component, because OpenID Connect

Jones, et al. Standards Track [Page 11] RFC 8414 OAuth 2.0 Authorization Server Metadata June 2018

 Discovery 1.0 specifies that the well-known URI string is appended to
 the issuer identifier (e.g.,
 "https://example.com/issuer1/.well-known/openid-configuration"),
 whereas this specification specifies that the well-known URI string
 is inserted before the path component of the issuer identifier (e.g.,
 "https://example.com/.well-known/openid-configuration/issuer1").
 Going forward, OAuth authorization server metadata locations should
 use the transformation defined in this specification.  However, when
 deployed in legacy environments in which the OpenID Connect Discovery
 1.0 transformation is already used, it may be necessary during a
 transition period to publish metadata for issuer identifiers
 containing a path component at both locations.  During this
 transition period, applications should first apply the transformation
 defined in this specification and attempt to retrieve the
 authorization server metadata from the resulting location; only if
 the retrieval from that location fails should they fall back to
 attempting to retrieve it from the alternate location obtained using
 the transformation defined by OpenID Connect Discovery 1.0.  This
 backwards-compatible behavior should only be necessary when the well-
 known URI suffix employed by the application is "openid-
 configuration".

6. Security Considerations

6.1. TLS Requirements

 Implementations MUST support TLS.  Which version(s) ought to be
 implemented will vary over time and depend on the widespread
 deployment and known security vulnerabilities at the time of
 implementation.  The authorization server MUST support TLS version
 1.2 [RFC5246] and MAY support additional TLS mechanisms meeting its
 security requirements.  When using TLS, the client MUST perform a
 TLS/SSL server certificate check, per RFC 6125 [RFC6125].
 Implementation security considerations can be found in
 "Recommendations for Secure Use of Transport Layer Security (TLS) and
 Datagram Transport Layer Security (DTLS)" [BCP195].
 To protect against information disclosure and tampering,
 confidentiality protection MUST be applied using TLS with a
 ciphersuite that provides confidentiality and integrity protection.

6.2. Impersonation Attacks

 TLS certificate checking MUST be performed by the client, as
 described in Section 6.1, when making an authorization server
 metadata request.  Checking that the server certificate is valid for
 the issuer identifier URL prevents man-in-middle and DNS-based

Jones, et al. Standards Track [Page 12] RFC 8414 OAuth 2.0 Authorization Server Metadata June 2018

 attacks.  These attacks could cause a client to be tricked into using
 an attacker's keys and endpoints, which would enable impersonation of
 the legitimate authorization server.  If an attacker can accomplish
 this, they can access the resources that the affected client has
 access to using the authorization server that they are impersonating.
 An attacker may also attempt to impersonate an authorization server
 by publishing a metadata document that contains an "issuer" claim
 using the issuer identifier URL of the authorization server being
 impersonated, but with its own endpoints and signing keys.  This
 would enable it to impersonate that authorization server, if accepted
 by the client.  To prevent this, the client MUST ensure that the
 issuer identifier URL it is using as the prefix for the metadata
 request exactly matches the value of the "issuer" metadata value in
 the authorization server metadata document received by the client.

6.3. Publishing Metadata in a Standard Format

 Publishing information about the authorization server in a standard
 format makes it easier for both legitimate clients and attackers to
 use the authorization server.  Whether an authorization server
 publishes its metadata in an ad hoc manner or in the standard format
 defined by this specification, the same defenses against attacks that
 might be mounted that use this information should be applied.

6.4. Protected Resources

 Secure determination of appropriate protected resources to use with
 an authorization server for all use cases is out of scope of this
 specification.  This specification assumes that the client has a
 means of determining appropriate protected resources to use with an
 authorization server and that the client is using the correct
 metadata for each authorization server.  Implementers need to be
 aware that if an inappropriate protected resource is used by the
 client, that an attacker may be able to act as a man-in-the-middle
 proxy to a valid protected resource without it being detected by the
 authorization server or the client.
 The ways to determine the appropriate protected resources to use with
 an authorization server are, in general, application dependent.  For
 instance, some authorization servers are used with a fixed protected
 resource or set of protected resources, the locations of which may be
 well known or could be published as metadata values by the
 authorization server.  In other cases, the set of resources that can
 be used with an authorization server can be dynamically changed by
 administrative actions.  Many other means of determining appropriate
 associations between authorization servers and protected resources
 are also possible.

Jones, et al. Standards Track [Page 13] RFC 8414 OAuth 2.0 Authorization Server Metadata June 2018

7. IANA Considerations

 The following registration procedure is used for the registry
 established by this specification.
 Values are registered on a Specification Required [RFC8126] basis
 after a two-week review period on the oauth-ext-review@ietf.org
 mailing list, on the advice of one or more Designated Experts.
 However, to allow for the allocation of values prior to publication,
 the Designated Experts may approve registration once they are
 satisfied that such a specification will be published.
 Registration requests sent to the mailing list for review should use
 an appropriate subject (e.g., "Request to register OAuth
 Authorization Server Metadata: example").
 Within the review period, the Designated Experts will either approve
 or deny the registration request, communicating this decision to the
 review list and IANA.  Denials should include an explanation and, if
 applicable, suggestions as to how to make the request successful.
 Registration requests that are undetermined for a period longer than
 21 days can be brought to the IESG's attention (using the
 iesg@ietf.org mailing list) for resolution.
 Criteria that should be applied by the Designated Experts include
 determining whether the proposed registration duplicates existing
 functionality, determining whether it is likely to be of general
 applicability or whether it is useful only for a single application,
 and whether the registration makes sense.
 IANA must only accept registry updates from the Designated Experts
 and should direct all requests for registration to the review mailing
 list.
 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
 Designated Expert, that Designated Expert should defer to the
 judgment of the other Designated Experts.

7.1. OAuth Authorization Server Metadata Registry

 This specification establishes the IANA "OAuth Authorization Server
 Metadata" registry for OAuth 2.0 authorization server metadata names.
 The registry records the authorization server metadata member and a
 reference to the specification that defines it.

Jones, et al. Standards Track [Page 14] RFC 8414 OAuth 2.0 Authorization Server Metadata June 2018

 The Designated Experts must either:
 (a) require that metadata names and values being registered use only
 printable ASCII characters excluding double quote ('"') and backslash
 ('\') (the Unicode characters with code points U+0021, U+0023 through
 U+005B, and U+005D through U+007E), or
 (b) if new metadata members or values are defined that use other code
 points, require that their definitions specify the exact sequences of
 Unicode code points used to represent them.  Furthermore, proposed
 registrations that use Unicode code points that can only be
 represented in JSON strings as escaped characters must not be
 accepted.

7.1.1. Registration Template

 Metadata Name:
    The name requested (e.g., "issuer").  This name is case-sensitive.
    Names may not match other registered names in a case-insensitive
    manner (one that would cause a match if the Unicode toLowerCase()
    operation were applied to both strings) unless the Designated
    Experts state that there is a compelling reason to allow an
    exception.
 Metadata Description:
    Brief description of the metadata (e.g., "Issuer identifier URL").
 Change Controller:
    For Standards Track RFCs, list the "IESG".  For others, give the
    name of the responsible party.  Other details (e.g., postal
    address, email address, home page URI) may also be included.
 Specification Document(s):
    Reference to the document or documents that specify the parameter,
    preferably including URIs that can be used to retrieve copies of
    the documents.  An indication of the relevant sections may also be
    included but is not required.

Jones, et al. Standards Track [Page 15] RFC 8414 OAuth 2.0 Authorization Server Metadata June 2018

7.1.2. Initial Registry Contents

 o  Metadata Name: issuer
 o  Metadata Description: Authorization server's issuer identifier URL
 o  Change Controller: IESG
 o  Specification Document(s): Section 2 of RFC 8414
 o  Metadata Name: authorization_endpoint
 o  Metadata Description: URL of the authorization server's
    authorization endpoint
 o  Change Controller: IESG
 o  Specification Document(s): Section 2 of RFC 8414
 o  Metadata Name: token_endpoint
 o  Metadata Description: URL of the authorization server's token
    endpoint
 o  Change Controller: IESG
 o  Specification Document(s): Section 2 of RFC 8414
 o  Metadata Name: jwks_uri
 o  Metadata Description: URL of the authorization server's JWK Set
    document
 o  Change Controller: IESG
 o  Specification Document(s): Section 2 of RFC 8414
 o  Metadata Name: registration_endpoint
 o  Metadata Description: URL of the authorization server's OAuth 2.0
    Dynamic Client Registration Endpoint
 o  Change Controller: IESG
 o  Specification Document(s): Section 2 of RFC 8414
 o  Metadata Name: scopes_supported
 o  Metadata Description: JSON array containing a list of the OAuth
    2.0 "scope" values that this authorization server supports
 o  Change Controller: IESG
 o  Specification Document(s): Section 2 of RFC 8414
 o  Metadata Name: response_types_supported
 o  Metadata Description: JSON array containing a list of the OAuth
    2.0 "response_type" values that this authorization server supports
 o  Change Controller: IESG
 o  Specification Document(s): Section 2 of RFC 8414
 o  Metadata Name: response_modes_supported
 o  Metadata Description: JSON array containing a list of the OAuth
    2.0 "response_mode" values that this authorization server supports
 o  Change Controller: IESG
 o  Specification Document(s): Section 2 of RFC 8414

Jones, et al. Standards Track [Page 16] RFC 8414 OAuth 2.0 Authorization Server Metadata June 2018

 o  Metadata Name: grant_types_supported
 o  Metadata Description: JSON array containing a list of the OAuth
    2.0 grant type values that this authorization server supports
 o  Change Controller: IESG
 o  Specification Document(s): Section 2 of RFC 8414
 o  Metadata Name: token_endpoint_auth_methods_supported
 o  Metadata Description: JSON array containing a list of client
    authentication methods supported by this token endpoint
 o  Change Controller: IESG
 o  Specification Document(s): Section 2 of RFC 8414
 o  Metadata Name: token_endpoint_auth_signing_alg_values_supported
 o  Metadata Description: JSON array containing a list of the JWS
    signing algorithms supported by the token endpoint for the
    signature on the JWT used to authenticate the client at the token
    endpoint
 o  Change Controller: IESG
 o  Specification Document(s): Section 2 of RFC 8414
 o  Metadata Name: service_documentation
 o  Metadata Description: URL of a page containing human-readable
    information that developers might want or need to know when using
    the authorization server
 o  Change Controller: IESG
 o  Specification Document(s): Section 2 of RFC 8414
 o  Metadata Name: ui_locales_supported
 o  Metadata Description: Languages and scripts supported for the user
    interface, represented as a JSON array of language tag values from
    BCP 47
 o  Change Controller: IESG
 o  Specification Document(s): Section 2 of RFC 8414
 o  Metadata Name: op_policy_uri
 o  Metadata Description: URL that the authorization server provides
    to the person registering the client to read about the
    authorization server's requirements on how the client can use the
    data provided by the authorization server
 o  Change Controller: IESG
 o  Specification Document(s): Section 2 of RFC 8414
 o  Metadata Name: op_tos_uri
 o  Metadata Description: URL that the authorization server provides
    to the person registering the client to read about the
    authorization server's terms of service
 o  Change Controller: IESG
 o  Specification Document(s): Section 2 of RFC 8414

Jones, et al. Standards Track [Page 17] RFC 8414 OAuth 2.0 Authorization Server Metadata June 2018

 o  Metadata Name: revocation_endpoint
 o  Metadata Description: URL of the authorization server's OAuth 2.0
    revocation endpoint
 o  Change Controller: IESG
 o  Specification Document(s): Section 2 of RFC 8414
 o  Metadata Name: revocation_endpoint_auth_methods_supported
 o  Metadata Description: JSON array containing a list of client
    authentication methods supported by this revocation endpoint
 o  Change Controller: IESG
 o  Specification Document(s): Section 2 of RFC 8414
 o  Metadata Name:
    revocation_endpoint_auth_signing_alg_values_supported
 o  Metadata Description: JSON array containing a list of the JWS
    signing algorithms supported by the revocation endpoint for the
    signature on the JWT used to authenticate the client at the
    revocation endpoint
 o  Change Controller: IESG
 o  Specification Document(s): Section 2 of RFC 8414
 o  Metadata Name: introspection_endpoint
 o  Metadata Description: URL of the authorization server's OAuth 2.0
    introspection endpoint
 o  Change Controller: IESG
 o  Specification Document(s): Section 2 of RFC 8414
 o  Metadata Name: introspection_endpoint_auth_methods_supported
 o  Metadata Description: JSON array containing a list of client
    authentication methods supported by this introspection endpoint
 o  Change Controller: IESG
 o  Specification Document(s): Section 2 of RFC 8414
 o  Metadata Name:
    introspection_endpoint_auth_signing_alg_values_supported
 o  Metadata Description: JSON array containing a list of the JWS
    signing algorithms supported by the introspection endpoint for the
    signature on the JWT used to authenticate the client at the
    introspection endpoint
 o  Change Controller: IESG
 o  Specification Document(s): Section 2 of RFC 8414
 o  Metadata Name: code_challenge_methods_supported
 o  Metadata Description: PKCE code challenge methods supported by
    this authorization server
 o  Change Controller: IESG
 o  Specification Document(s): Section 2 of RFC 8414

Jones, et al. Standards Track [Page 18] RFC 8414 OAuth 2.0 Authorization Server Metadata June 2018

 o  Metadata Name: signed_metadata
 o  Metadata Description: Signed JWT containing metadata values about
    the authorization server as claims
 o  Change Controller: IESG
 o  Specification Document(s): Section 2.1 of RFC 8414

7.2. Updated Registration Instructions

 This specification adds to the instructions for the Designated
 Experts of the following IANA registries, both of which are in the
 "OAuth Parameters" registry [IANA.OAuth.Parameters]:
 o  OAuth Access Token Types
 o  OAuth Token Endpoint Authentication Methods
 IANA has added a link to this specification in the Reference sections
 of these registries.
 For these registries, the Designated Experts must reject registration
 requests in one registry for values already occurring in the other
 registry.  This is necessary because the
 "introspection_endpoint_auth_methods_supported" parameter allows for
 the use of values from either registry.  That way, because the values
 in the two registries will continue to be mutually exclusive, no
 ambiguities will arise.

7.3. Well-Known URI Registry

 This specification registers the well-known URI defined in Section 3
 in the IANA "Well-Known URIs" registry [IANA.well-known] established
 by RFC 5785 [RFC5785].

7.3.1. Registry Contents

 o  URI suffix: oauth-authorization-server
 o  Change controller: IESG
 o  Specification document: Section 3 of RFC 8414
 o  Related information: (none)

Jones, et al. Standards Track [Page 19] RFC 8414 OAuth 2.0 Authorization Server Metadata June 2018

8. References

8.1. Normative References

 [BCP195]   Sheffer, Y., Holz, R., and P. Saint-Andre,
            "Recommendations for Secure Use of Transport Layer
            Security (TLS) and Datagram Transport Layer Security
            (DTLS)", BCP 195, RFC 7525, May 2015,
            <http://www.rfc-editor.org/info/bcp195>.
 [IANA.OAuth.Parameters]
            IANA, "OAuth Parameters",
            <https://www.iana.org/assignments/oauth-parameters>.
 [JWE]      Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)",
            RFC 7516, DOI 10.17487/RFC7516, May 2015,
            <https://www.rfc-editor.org/info/rfc7516>.
 [JWK]      Jones, M., "JSON Web Key (JWK)", RFC 7517,
            DOI 10.17487/RFC7517, May 2015,
            <https://www.rfc-editor.org/info/rfc7517>.
 [JWS]      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>.
 [JWT]      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>.
 [OAuth.Post]
            Jones, M. and B. Campbell, "OAuth 2.0 Form Post Response
            Mode", April 2015, <http://openid.net/specs/
            oauth-v2-form-post-response-mode-1_0.html>.
 [OAuth.Responses]
            de Medeiros, B., Ed., Scurtescu, M., Tarjan, P., and M.
            Jones, "OAuth 2.0 Multiple Response Type Encoding
            Practices", February 2014, <http://openid.net/specs/
            oauth-v2-multiple-response-types-1_0.html>.
 [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>.

Jones, et al. Standards Track [Page 20] RFC 8414 OAuth 2.0 Authorization Server Metadata June 2018

 [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>.
 [RFC5646]  Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying
            Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646,
            September 2009, <https://www.rfc-editor.org/info/rfc5646>.
 [RFC5785]  Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known
            Uniform Resource Identifiers (URIs)", RFC 5785,
            DOI 10.17487/RFC5785, April 2010,
            <https://www.rfc-editor.org/info/rfc5785>.
 [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>.
 [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>.
 [RFC7009]  Lodderstedt, T., Ed., Dronia, S., and M. Scurtescu, "OAuth
            2.0 Token Revocation", RFC 7009, DOI 10.17487/RFC7009,
            August 2013, <https://www.rfc-editor.org/info/rfc7009>.
 [RFC7033]  Jones, P., Salgueiro, G., Jones, M., and J. Smarr,
            "WebFinger", RFC 7033, DOI 10.17487/RFC7033, September
            2013, <https://www.rfc-editor.org/info/rfc7033>.
 [RFC7591]  Richer, J., Ed., Jones, M., Bradley, J., Machulak, M., and
            P. Hunt, "OAuth 2.0 Dynamic Client Registration Protocol",
            RFC 7591, DOI 10.17487/RFC7591, July 2015,
            <https://www.rfc-editor.org/info/rfc7591>.
 [RFC7636]  Sakimura, N., Ed., Bradley, J., and N. Agarwal, "Proof Key
            for Code Exchange by OAuth Public Clients", RFC 7636,
            DOI 10.17487/RFC7636, September 2015,
            <https://www.rfc-editor.org/info/rfc7636>.
 [RFC7662]  Richer, J., Ed., "OAuth 2.0 Token Introspection",
            RFC 7662, DOI 10.17487/RFC7662, October 2015,
            <https://www.rfc-editor.org/info/rfc7662>.

Jones, et al. Standards Track [Page 21] RFC 8414 OAuth 2.0 Authorization Server Metadata June 2018

 [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>.
 [UNICODE]  The Unicode Consortium, "The Unicode Standard",
            <http://www.unicode.org/versions/latest/>.
 [USA15]    Davis, M., Ed. and K. Whistler, Ed., "Unicode
            Normalization Forms", Unicode Standard Annex #15, May
            2018, <http://www.unicode.org/reports/tr15/>.

8.2. Informative References

 [IANA.well-known]
            IANA, "Well-Known URIs",
            <https://www.iana.org/assignments/well-known-uris>.
 [MIX-UP]   Jones, M., Bradley, J., and N. Sakimura, "OAuth 2.0 Mix-Up
            Mitigation", Work in Progress, draft-ietf-oauth-mix-up-
            mitigation-01, July 2016.
 [OpenID.Core]
            Sakimura, N., Bradley, J., Jones, M., de Medeiros, B., and
            C. Mortimore, "OpenID Connect Core 1.0", November 2014,
            <http://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", November 2014,
            <http://openid.net/specs/
            openid-connect-discovery-1_0.html>.
 [OpenID.Registration]
            Sakimura, N., Bradley, J., and M. Jones, "OpenID Connect
            Dynamic Client Registration 1.0", November 2014,
            <http://openid.net/specs/
            openid-connect-registration-1_0.html>.

Jones, et al. Standards Track [Page 22] RFC 8414 OAuth 2.0 Authorization Server Metadata June 2018

Acknowledgements

 This specification is based on the OpenID Connect Discovery 1.0
 specification, which was produced by the OpenID Connect working group
 of the OpenID Foundation.  This specification standardizes the de
 facto usage of the metadata format defined by OpenID Connect
 Discovery to publish OAuth authorization server metadata.
 The authors would like to thank the following people for their
 reviews of this specification: Shwetha Bhandari, Ben Campbell, Brian
 Campbell, Brian Carpenter, William Denniss, Vladimir Dzhuvinov,
 Donald Eastlake, Samuel Erdtman, George Fletcher, Dick Hardt, Phil
 Hunt, Alexey Melnikov, Tony Nadalin, Mark Nottingham, Eric Rescorla,
 Justin Richer, Adam Roach, Hannes Tschofenig, and Hans Zandbelt.

Authors' Addresses

 Michael B. Jones
 Microsoft
 Email: mbj@microsoft.com
 URI:   http://self-issued.info/
 Nat Sakimura
 Nomura Research Institute, Ltd.
 Email: n-sakimura@nri.co.jp
 URI:   http://nat.sakimura.org/
 John Bradley
 Yubico
 Email: RFC8414@ve7jtb.com
 URI:   http://www.thread-safe.com/

Jones, et al. Standards Track [Page 23]

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