





Internet Engineering Task Force (IETF)                    J. Richer, Ed.
Request for Comments: 7591
Category: Standards Track                                       M. Jones
ISSN: 2070-1721                                                Microsoft
                                                              J. Bradley
                                                           Ping Identity
                                                             M. Machulak
                                                    Newcastle University
                                                                 P. Hunt
                                                      Oracle Corporation
                                                               July 2015


             OAuth 2.0 Dynamic Client Registration Protocol

Abstract

   This specification defines mechanisms for dynamically registering
   OAuth 2.0 clients with authorization servers.  Registration requests
   send a set of desired client metadata values to the authorization
   server.  The resulting registration responses return a client
   identifier to use at the authorization server and the client metadata
   values registered for the client.  The client can then use this
   registration information to communicate with the authorization server
   using the OAuth 2.0 protocol.  This specification also defines a set
   of common client metadata fields and values for clients to use during
   registration.

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 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7591.










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Copyright Notice

   Copyright (c) 2015 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
   (http://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.





































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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . .   4
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
     1.3.  Protocol Flow . . . . . . . . . . . . . . . . . . . . . .   7
   2.  Client Metadata . . . . . . . . . . . . . . . . . . . . . . .   8
     2.1.  Relationship between Grant Types and Response Types . . .  12
     2.2.  Human-Readable Client Metadata  . . . . . . . . . . . . .  13
     2.3.  Software Statement  . . . . . . . . . . . . . . . . . . .  14
   3.  Client Registration Endpoint  . . . . . . . . . . . . . . . .  15
     3.1.  Client Registration Request . . . . . . . . . . . . . . .  16
       3.1.1.  Client Registration Request Using a Software
               Statement . . . . . . . . . . . . . . . . . . . . . .  18
     3.2.  Responses . . . . . . . . . . . . . . . . . . . . . . . .  19
       3.2.1.  Client Information Response . . . . . . . . . . . . .  19
       3.2.2.  Client Registration Error Response  . . . . . . . . .  21
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  23
     4.1.  OAuth Dynamic Client Registration Metadata Registry . . .  22
       4.1.1.  Registration Template . . . . . . . . . . . . . . . .  24
       4.1.2.  Initial Registry Contents . . . . . . . . . . . . . .  24
     4.2.  OAuth Token Endpoint Authentication Methods Registry  . .  27
       4.2.1.  Registration Template . . . . . . . . . . . . . . . .  28
       4.2.2.  Initial Registry Contents . . . . . . . . . . . . . .  28
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  28
   6.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  32
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  33
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  33
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  35
   Appendix A.  Use Cases  . . . . . . . . . . . . . . . . . . . . .  33
     A.1.  Open versus Protected Dynamic Client Registration . . . .  34
       A.1.1.  Open Dynamic Client Registration  . . . . . . . . . .  34
       A.1.2.  Protected Dynamic Client Registration . . . . . . . .  34
     A.2.  Registration without or with Software Statements  . . . .  34
       A.2.1.  Registration without a Software Statement . . . . . .  34
       A.2.2.  Registration with a Software Statement  . . . . . . .  34
     A.3.  Registration by the Client or Developer . . . . . . . . .  34
       A.3.1.  Registration by the Client  . . . . . . . . . . . . .  35
       A.3.2.  Registration by the Developer . . . . . . . . . . . .  35
     A.4.  Client ID per Client Instance or per Client Software  . .  35
       A.4.1.  Client ID per Client Software Instance  . . . . . . .  35
       A.4.2.  Client ID Shared among All Instances of Client
               Software  . . . . . . . . . . . . . . . . . . . . . .  35
     A.5.  Stateful or Stateless Registration  . . . . . . . . . . .  35
       A.5.1.  Stateful Client Registration  . . . . . . . . . . . .  36
       A.5.2.  Stateless Client Registration . . . . . . . . . . . .  36
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  36
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  36



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1.  Introduction

   In order for an OAuth 2.0 [RFC6749] client to utilize an OAuth 2.0
   authorization server, the client needs specific information to
   interact with the server, including an OAuth 2.0 client identifier to
   use at that server.  This specification describes how an OAuth 2.0
   client can be dynamically registered with an authorization server to
   obtain this information.

   As part of the registration process, this specification also defines
   a mechanism for the client to present the authorization server with a
   set of metadata, such as a set of valid redirection URIs.  This
   metadata can either be communicated in a self-asserted fashion or as
   a set of metadata called a software statement, which is digitally
   signed or protected with a Message Authentication Code (MAC); in the
   case of a software statement, the issuer is vouching for the validity
   of the data about the client.

   Traditionally, registration of a client with an authorization server
   is performed manually.  The mechanisms defined in this specification
   can be used either for a client to dynamically register itself with
   authorization servers or for a client developer to programmatically
   register the client with authorization servers.  Multiple
   applications using OAuth 2.0 have previously developed mechanisms for
   accomplishing such registrations.  This specification generalizes the
   registration mechanisms defined by "OpenID Connect Dynamic Client
   Registration 1.0" [OpenID.Registration] and used by "User Managed
   Access (UMA) Profile of OAuth 2.0" [UMA-Core] in a way that is
   compatible with both, while being applicable to a wider set of OAuth
   2.0 use cases.

1.1.  Notational Conventions

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

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

1.2.  Terminology

   This specification uses the terms "access token", "authorization
   code", "authorization endpoint", "authorization grant",
   "authorization server", "client", "client identifier", "client
   secret", "grant type", "protected resource", "redirection URI",





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   "refresh token", "resource owner", "resource server", "response
   type", and "token endpoint" defined by OAuth 2.0 [RFC6749] and uses
   the term "Claim" defined by JSON Web Token (JWT) [RFC7519].

   This specification defines the following terms:

   Client Software
      Software implementing an OAuth 2.0 client.

   Client Instance
      A deployed instance of a piece of client software.

   Client Developer
      The person or organization that builds a client software package
      and prepares it for distribution.  At the time the client is
      built, the developer is often not aware of who the deploying
      service provider organizations will be.  Client developers will
      need to use dynamic registration when they are unable to predict
      aspects of the software, such as the deployment URLs, at compile
      time.  For instance, this can occur when the software API
      publisher and the deploying organization are not the same.

   Client Registration Endpoint
      OAuth 2.0 endpoint through which a client can be registered at an
      authorization server.  The means by which the URL for this
      endpoint is obtained are out of scope for this specification.

   Initial Access Token
      OAuth 2.0 access token optionally issued by an authorization
      server to a developer or client and used to authorize calls to the
      client registration endpoint.  The type and format of this token
      are likely service specific and are out of scope for this
      specification.  The means by which the authorization server issues
      this token as well as the means by which the registration endpoint
      validates this token are out of scope for this specification.  Use
      of an initial access token is required when the authorization
      server limits the parties that can register a client.

   Deployment Organization
      An administrative security domain under which a software API
      (service) is deployed and protected by an OAuth 2.0 framework.  In
      some OAuth scenarios, the deployment organization and the software
      API publisher are the same.  In these cases, the deploying
      organization will often have a close relationship with client
      software developers.  In many other cases, the definer of the
      service may be an independent third-party publisher or a standards
      organization.  When working to a published specification for an




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      API, the client software developer is unable to have a prior
      relationship with the potentially many deployment organizations
      deploying the software API (service).

   Software API Deployment
      A deployed instance of a software API that is protected by OAuth
      2.0 (a protected resource) in a particular deployment organization
      domain.  For any particular software API, there may be one or more
      deployments.  A software API deployment typically has an
      associated OAuth 2.0 authorization server as well as a client
      registration endpoint.  The means by which endpoints are obtained
      are out of scope for this specification.

   Software API Publisher
      The organization that defines a particular web-accessible API that
      may be deployed in one or more deployment environments.  A
      publisher may be any standards body, commercial, public, private,
      or open source organization that is responsible for publishing and
      distributing software and API specifications that may be protected
      via OAuth 2.0.  In some cases, a software API publisher and a
      client developer may be the same organization.  At the time of
      publication of a web-accessible API, the software publisher often
      does not have a prior relationship with the deploying
      organizations.

   Software Statement
      A digitally signed or MACed JSON Web Token (JWT) [RFC7519] that
      asserts metadata values about the client software.  In some cases,
      a software statement will be issued directly by the client
      developer.  In other cases, a software statement will be issued by
      a third-party organization for use by the client developer.  In
      both cases, the trust relationship the authorization server has
      with the issuer of the software statement is intended to be used
      as an input to the evaluation of whether the registration request
      is accepted.  A software statement can be presented to an
      authorization server as part of a client registration request.















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1.3.  Protocol Flow

        +--------(A)- Initial Access Token (OPTIONAL)
        |
        |   +----(B)- Software Statement (OPTIONAL)
        |   |
        v   v
    +-----------+                                      +---------------+
    |           |--(C)- Client Registration Request -->|    Client     |
    | Client or |                                      | Registration  |
    | Developer |<-(D)- Client Information Response ---|   Endpoint    |
    |           |        or Client Error Response      +---------------+
    +-----------+

   Figure 1: Abstract Dynamic Client Registration Flow

   The abstract OAuth 2.0 client dynamic registration flow illustrated
   in Figure 1 describes the interaction between the client or developer
   and the endpoint defined in this specification.  This figure does not
   demonstrate error conditions.  This flow includes the following
   steps:

   (A)   Optionally, the client or developer is issued an initial access
         token giving access to the client registration endpoint.  The
         method by which the initial access token is issued to the
         client or developer is out of scope for this specification.

   (B)   Optionally, the client or developer is issued a software
         statement for use with the client registration endpoint.  The
         method by which the software statement is issued to the client
         or developer is out of scope for this specification.

   (C)   The client or developer calls the client registration endpoint
         with the client's desired registration metadata, optionally
         including the initial access token from (A) if one is required
         by the authorization server.

   (D)   The authorization server registers the client and returns:

         *  the client's registered metadata,

         *  a client identifier that is unique at the server, and

         *  a set of client credentials such as a client secret, if
            applicable for this client.

   Examples of different configurations and usages are included in
   Appendix A.



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2.  Client Metadata

   Registered clients have a set of metadata values associated with
   their client identifier at an authorization server, such as the list
   of valid redirection URIs or a display name.

   These client metadata values are used in two ways:

   o  as input values to registration requests, and

   o  as output values in registration responses.

   The following client metadata fields are defined by this
   specification.  The implementation and use of all client metadata
   fields is OPTIONAL, unless stated otherwise.  All data member types
   (strings, arrays, numbers) are defined in terms of their JSON
   [RFC7159] representations.

   redirect_uris
      Array of redirection URI strings for use in redirect-based flows
      such as the authorization code and implicit flows.  As required by
      Section 2 of OAuth 2.0 [RFC6749], clients using flows with
      redirection MUST register their redirection URI values.
      Authorization servers that support dynamic registration for
      redirect-based flows MUST implement support for this metadata
      value.

   token_endpoint_auth_method
      String indicator of the requested authentication method for the
      token endpoint.  Values defined by this specification are:

      *  "none": The client is a public client as defined in OAuth 2.0,
         Section 2.1, and does not have a client secret.

      *  "client_secret_post": The client uses the HTTP POST parameters
         as defined in OAuth 2.0, Section 2.3.1.

      *  "client_secret_basic": The client uses HTTP Basic as defined in
         OAuth 2.0, Section 2.3.1.

      Additional values can be defined via the IANA "OAuth Token
      Endpoint Authentication Methods" registry established in
      Section 4.2.  Absolute URIs can also be used as values for this
      parameter without being registered.  If unspecified or omitted,
      the default is "client_secret_basic", denoting the HTTP Basic
      authentication scheme as specified in Section 2.3.1 of OAuth 2.0.





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   grant_types
      Array of OAuth 2.0 grant type strings that the client can use at
      the token endpoint.  These grant types are defined as follows:

      *  "authorization_code": The authorization code grant type defined
         in OAuth 2.0, Section 4.1.

      *  "implicit": The implicit grant type defined in OAuth 2.0,
         Section 4.2.

      *  "password": The resource owner password credentials grant type
         defined in OAuth 2.0, Section 4.3.

      *  "client_credentials": The client credentials grant type defined
         in OAuth 2.0, Section 4.4.

      *  "refresh_token": The refresh token grant type defined in OAuth
         2.0, Section 6.

      *  "urn:ietf:params:oauth:grant-type:jwt-bearer": The JWT Bearer
         Token Grant Type defined in OAuth JWT Bearer Token Profiles
         [RFC7523].

      *  "urn:ietf:params:oauth:grant-type:saml2-bearer": The SAML 2.0
         Bearer Assertion Grant defined in OAuth SAML 2 Bearer Token
         Profiles [RFC7522].

      If the token endpoint is used in the grant type, the value of this
      parameter MUST be the same as the value of the "grant_type"
      parameter passed to the token endpoint defined in the grant type
      definition.  Authorization servers MAY allow for other values as
      defined in the grant type extension process described in OAuth
      2.0, Section 4.5.  If omitted, the default behavior is that the
      client will use only the "authorization_code" Grant Type.

   response_types
      Array of the OAuth 2.0 response type strings that the client can
      use at the authorization endpoint.  These response types are
      defined as follows:

      *  "code": The authorization code response type defined in OAuth
         2.0, Section 4.1.

      *  "token": The implicit response type defined in OAuth 2.0,
         Section 4.2.






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      If the authorization endpoint is used by the grant type, the value
      of this parameter MUST be the same as the value of the
      "response_type" parameter passed to the authorization endpoint
      defined in the grant type definition.  Authorization servers MAY
      allow for other values as defined in the grant type extension
      process is described in OAuth 2.0, Section 4.5.  If omitted, the
      default is that the client will use only the "code" response type.

   client_name
      Human-readable string name of the client to be presented to the
      end-user during authorization.  If omitted, the authorization
      server MAY display the raw "client_id" value to the end-user
      instead.  It is RECOMMENDED that clients always send this field.
      The value of this field MAY be internationalized, as described in
      Section 2.2.

   client_uri
      URL string of a web page providing information about the client.
      If present, the server SHOULD display this URL to the end-user in
      a clickable fashion.  It is RECOMMENDED that clients always send
      this field.  The value of this field MUST point to a valid web
      page.  The value of this field MAY be internationalized, as
      described in Section 2.2.

   logo_uri
      URL string that references a logo for the client.  If present, the
      server SHOULD display this image to the end-user during approval.
      The value of this field MUST point to a valid image file.  The
      value of this field MAY be internationalized, as described in
      Section 2.2.

   scope
      String containing a space-separated list of scope values (as
      described in Section 3.3 of OAuth 2.0 [RFC6749]) that the client
      can use when requesting access tokens.  The semantics of values in
      this list are service specific.  If omitted, an authorization
      server MAY register a client with a default set of scopes.

   contacts
      Array of strings representing ways to contact people responsible
      for this client, typically email addresses.  The authorization
      server MAY make these contact addresses available to end-users for
      support requests for the client.  See Section 6 for information on
      Privacy Considerations.







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   tos_uri
      URL string that points to a human-readable terms of service
      document for the client that describes a contractual relationship
      between the end-user and the client that the end-user accepts when
      authorizing the client.  The authorization server SHOULD display
      this URL to the end-user if it is provided.  The value of this
      field MUST point to a valid web page.  The value of this field MAY
      be internationalized, as described in Section 2.2.

   policy_uri
      URL string that points to a human-readable privacy policy document
      that describes how the deployment organization collects, uses,
      retains, and discloses personal data.  The authorization server
      SHOULD display this URL to the end-user if it is provided.  The
      value of this field MUST point to a valid web page.  The value of
      this field MAY be internationalized, as described in Section 2.2.

   jwks_uri
      URL string referencing the client's JSON Web Key (JWK) Set
      [RFC7517] document, which contains the client's public keys.  The
      value of this field MUST point to a valid JWK Set document.  These
      keys can be used by higher-level protocols that use signing or
      encryption.  For instance, these keys might be used by some
      applications for validating signed requests made to the token
      endpoint when using JWTs for client authentication [RFC7523].  Use
      of this parameter is preferred over the "jwks" parameter, as it
      allows for easier key rotation.  The "jwks_uri" and "jwks"
      parameters MUST NOT both be present in the same request or
      response.

   jwks
      Client's JSON Web Key Set [RFC7517] document value, which contains
      the client's public keys.  The value of this field MUST be a JSON
      object containing a valid JWK Set.  These keys can be used by
      higher-level protocols that use signing or encryption.  This
      parameter is intended to be used by clients that cannot use the
      "jwks_uri" parameter, such as native clients that cannot host
      public URLs.  The "jwks_uri" and "jwks" parameters MUST NOT both
      be present in the same request or response.

   software_id
      A unique identifier string (e.g., a Universally Unique Identifier
      (UUID)) assigned by the client developer or software publisher
      used by registration endpoints to identify the client software to
      be dynamically registered.  Unlike "client_id", which is issued by
      the authorization server and SHOULD vary between instances, the
      "software_id" SHOULD remain the same for all instances of the
      client software.  The "software_id" SHOULD remain the same across



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      multiple updates or versions of the same piece of software.  The
      value of this field is not intended to be human readable and is
      usually opaque to the client and authorization server.

   software_version
      A version identifier string for the client software identified by
      "software_id".  The value of the "software_version" SHOULD change
      on any update to the client software identified by the same
      "software_id".  The value of this field is intended to be compared
      using string equality matching and no other comparison semantics
      are defined by this specification.  The value of this field is
      outside the scope of this specification, but it is not intended to
      be human readable and is usually opaque to the client and
      authorization server.  The definition of what constitutes an
      update to client software that would trigger a change to this
      value is specific to the software itself and is outside the scope
      of this specification.

   Extensions and profiles of this specification can expand this list
   with metadata names and descriptions registered in accordance with
   the IANA Considerations in Section 4 of this document.  The
   authorization server MUST ignore any client metadata sent by the
   client that it does not understand (for instance, by silently
   removing unknown metadata from the client's registration record
   during processing).  The authorization server MAY reject any
   requested client metadata values by replacing requested values with
   suitable defaults as described in Section 3.2.1 or by returning an
   error response as described in Section 3.2.2.

   Client metadata values can be either communicated directly in the
   body of a registration request, as described in Section 3.1, or
   included as claims in a software statement, as described in
   Section 2.3; a mixture of both is also possible.  If the same client
   metadata name is present in both locations and the software statement
   is trusted by the authorization server, the value of a claim in the
   software statement MUST take precedence.

2.1.  Relationship between Grant Types and Response Types

   The "grant_types" and "response_types" values described above are
   partially orthogonal, as they refer to arguments passed to different
   endpoints in the OAuth protocol.  However, they are related in that
   the "grant_types" available to a client influence the
   "response_types" that the client is allowed to use, and vice versa.
   For instance, a "grant_types" value that includes
   "authorization_code" implies a "response_types" value that includes
   "code", as both values are defined as part of the OAuth 2.0
   authorization code grant.  As such, a server supporting these fields



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   SHOULD take steps to ensure that a client cannot register itself into
   an inconsistent state, for example, by returning an
   "invalid_client_metadata" error response to an inconsistent
   registration request.

   The correlation between the two fields is listed in the table below.

   +-----------------------------------------------+-------------------+
   | grant_types value includes:                   | response_types    |
   |                                               | value includes:   |
   +-----------------------------------------------+-------------------+
   | authorization_code                            | code              |
   | implicit                                      | token             |
   | password                                      | (none)            |
   | client_credentials                            | (none)            |
   | refresh_token                                 | (none)            |
   | urn:ietf:params:oauth:grant-type:jwt-bearer   | (none)            |
   | urn:ietf:params:oauth:grant-type:saml2-bearer | (none)            |
   +-----------------------------------------------+-------------------+

   Extensions and profiles of this document that introduce new values to
   either the "grant_types" or "response_types" parameter MUST document
   all correspondences between these two parameter types.

2.2.  Human-Readable Client Metadata

   Human-readable client metadata values and client metadata values that
   reference human-readable values MAY be represented in multiple
   languages and scripts.  For example, the values of fields such as
   "client_name", "tos_uri", "policy_uri", "logo_uri", and "client_uri"
   might have multiple locale-specific values in some client
   registrations to facilitate use in different locations.

   To specify the languages and scripts, BCP 47 [RFC5646] language tags
   are added to client metadata member names, delimited by a "#"
   character.  Since JSON [RFC7159] member names are case sensitive, it
   is RECOMMENDED that language tag values used in Claim Names be
   spelled using the character case with which they are registered in
   the "IANA Language Subtag" registry [IANA.Language].  In particular,
   normally language names are spelled with lowercase characters, region
   names are spelled with uppercase characters, and languages are
   spelled with mixed-case characters.  However, since BCP 47 language
   tag values are case-insensitive, implementations SHOULD interpret the
   language tag values supplied in a case insensitive manner.  Per the
   recommendations in BCP 47, language tag values used in metadata
   member names should only be as specific as necessary.  For instance,
   using "fr" might be sufficient in many contexts, rather than "fr-CA"
   or "fr-FR".



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   For example, a client could represent its name in English as
   "client_name#en": "My Client" and its name in Japanese as
   "client_name#ja-Jpan-JP":
   "\u30AF\u30E9\u30A4\u30A2\u30F3\u30C8\u540D" within the same
   registration request.  The authorization server MAY display any or
   all of these names to the resource owner during the authorization
   step, choosing which name to display based on system configuration,
   user preferences or other factors.

   If any human-readable field is sent without a language tag, parties
   using it MUST NOT make any assumptions about the language, character
   set, or script of the string value, and the string value MUST be used
   as is wherever it is presented in a user interface.  To facilitate
   interoperability, it is RECOMMENDED that clients and servers use a
   human-readable field without any language tags in addition to any
   language-specific fields, and it is RECOMMENDED that any human-
   readable fields sent without language tags contain values suitable
   for display on a wide variety of systems.

   Implementer's Note: Many JSON libraries make it possible to reference
   members of a JSON object as members of an object construct in the
   native programming environment of the library.  However, while the
   "#" character is a valid character inside of a JSON object's member
   names, it is not a valid character for use in an object member name
   in many programming environments.  Therefore, implementations will
   need to use alternative access forms for these claims.  For instance,
   in JavaScript, if one parses the JSON as follows, "var j =
   JSON.parse(json);", then as a workaround the member
   "client_name#en-us" can be accessed using the JavaScript syntax
   "j["client_name#en-us"]".

2.3.  Software Statement

   A software statement is a JSON Web Token (JWT) [RFC7519] that asserts
   metadata values about the client software as a bundle.  A set of
   claims that can be used in a software statement are defined in
   Section 2.  When presented to the authorization server as part of a
   client registration request, the software statement MUST be digitally
   signed or MACed using JSON Web Signature (JWS) [RFC7515] and MUST
   contain an "iss" (issuer) claim denoting the party attesting to the
   claims in the software statement.  It is RECOMMENDED that software
   statements be digitally signed using the "RS256" signature algorithm,
   although particular applications MAY specify the use of different
   algorithms.  It is RECOMMENDED that software statements contain the
   "software_id" claim to allow authorization servers to correlate
   different instances of software using the same software statement.





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   For example, a software statement could contain the following claims:

     {
      "software_id": "4NRB1-0XZABZI9E6-5SM3R",
      "client_name": "Example Statement-based Client",
      "client_uri": "https://client.example.net/"
     }

   The following non-normative example JWT includes these claims and has
   been asymmetrically signed using "RS256" (with line breaks for
   display purposes only):

     eyJhbGciOiJSUzI1NiJ9.
     eyJzb2Z0d2FyZV9pZCI6IjROUkIxLTBYWkFCWkk5RTYtNVNNM1IiLCJjbGll
     bnRfbmFtZSI6IkV4YW1wbGUgU3RhdGVtZW50LWJhc2VkIENsaWVudCIsImNs
     aWVudF91cmkiOiJodHRwczovL2NsaWVudC5leGFtcGxlLm5ldC8ifQ.
     GHfL4QNIrQwL18BSRdE595T9jbzqa06R9BT8w409x9oIcKaZo_mt15riEXHa
     zdISUvDIZhtiyNrSHQ8K4TvqWxH6uJgcmoodZdPwmWRIEYbQDLqPNxREtYn0
     5X3AR7ia4FRjQ2ojZjk5fJqJdQ-JcfxyhK-P8BAWBd6I2LLA77IG32xtbhxY
     fHX7VhuU5ProJO8uvu3Ayv4XRhLZJY4yKfmyjiiKiPNe-Ia4SMy_d_QSWxsk
     U5XIQl5Sa2YRPMbDRXttm2TfnZM1xx70DoYi8g6czz-CPGRi4SW_S2RKHIJf
     IjoI3zTJ0Y2oe0_EJAiXbL6OyF9S5tKxDXV8JIndSA

   The software statement is typically distributed with all instances of
   a client application.  The means by which a client or developer
   obtains a software statement are outside the scope of this
   specification.  Some common methods could include a client developer
   generating a client-specific JWT by registering with a software API
   publisher to obtain a software statement for a class of clients.

   The criteria by which authorization servers determine whether to
   trust and utilize the information in a software statement are outside
   the scope of this specification.

   In some cases, authorization servers MAY choose to accept a software
   statement value directly as a client identifier in an authorization
   request, without a prior dynamic client registration having been
   performed.  The circumstances under which an authorization server
   would do so, and the specific software statement characteristics
   required in this case, are outside the scope of this specification.

3.  Client Registration Endpoint

   The client registration endpoint is an OAuth 2.0 endpoint defined in
   this document that is designed to allow a client to be registered
   with the authorization server.  The client registration endpoint MUST
   accept HTTP POST messages with request parameters encoded in the




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   entity body using the "application/json" format.  The client
   registration endpoint MUST be protected by a transport-layer security
   mechanism, as described in Section 5.

   The client registration endpoint MAY be an OAuth 2.0 [RFC6749]
   protected resource and it MAY accept an initial access token in the
   form of an OAuth 2.0 access token to limit registration to only
   previously authorized parties.  The method by which the initial
   access token is obtained by the client or developer is generally out
   of band and is out of scope for this specification.  The method by
   which the initial access token is verified and validated by the
   client registration endpoint is out of scope for this specification.

   To support open registration and facilitate wider interoperability,
   the client registration endpoint SHOULD allow registration requests
   with no authorization (which is to say, with no initial access token
   in the request).  These requests MAY be rate-limited or otherwise
   limited to prevent a denial-of-service attack on the client
   registration endpoint.

3.1.  Client Registration Request

   This operation registers a client with the authorization server.  The
   authorization server assigns this client a unique client identifier,
   optionally assigns a client secret, and associates the metadata
   provided in the request with the issued client identifier.  The
   request includes any client metadata parameters being specified for
   the client during the registration.  The authorization server MAY
   provision default values for any items omitted in the client
   metadata.

   To register, the client or developer sends an HTTP POST to the client
   registration endpoint with a content type of "application/json".  The
   HTTP Entity Payload is a JSON [RFC7159] document consisting of a JSON
   object and all requested client metadata values as top-level members
   of that JSON object.

   For example, if the server supports open registration (with no
   initial access token), the client could send the following
   registration request to the client registration endpoint.











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   The following is a non-normative example request not using an initial
   access token:

     POST /register HTTP/1.1
     Content-Type: application/json
     Accept: application/json
     Host: server.example.com

     {
      "redirect_uris": [
        "https://client.example.org/callback",
        "https://client.example.org/callback2"],
      "client_name": "My Example Client",
      "client_name#ja-Jpan-JP":
         "\u30AF\u30E9\u30A4\u30A2\u30F3\u30C8\u540D",
      "token_endpoint_auth_method": "client_secret_basic",
      "logo_uri": "https://client.example.org/logo.png",
      "jwks_uri": "https://client.example.org/my_public_keys.jwks",
      "example_extension_parameter": "example_value"
     }

   Alternatively, if the server supports authorized registration, the
   developer or the client will be provisioned with an initial access
   token.  (The method by which the initial access token is obtained is
   out of scope for this specification.)  The developer or client sends
   the following authorized registration request to the client
   registration endpoint.  Note that the initial access token sent in
   this example as an OAuth 2.0 Bearer Token [RFC6750], but any OAuth
   2.0 token type could be used by an authorization server.






















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   The following is a non-normative example request using an initial
   access token and registering a JWK Set by value (with line breaks
   within values for display purposes only):

     POST /register HTTP/1.1
     Content-Type: application/json
     Accept: application/json
     Authorization: Bearer ey23f2.adfj230.af32-developer321
     Host: server.example.com

     {
      "redirect_uris": ["https://client.example.org/callback",
         "https://client.example.org/callback2"],
      "client_name": "My Example Client",
      "client_name#ja-Jpan-JP":
         "\u30AF\u30E9\u30A4\u30A2\u30F3\u30C8\u540D",
      "token_endpoint_auth_method": "client_secret_basic",
      "policy_uri": "https://client.example.org/policy.html",
      "jwks": {"keys": [{
         "e": "AQAB",
         "n": "nj3YJwsLUFl9BmpAbkOswCNVx17Eh9wMO-_AReZwBqfaWFcfG
   HrZXsIV2VMCNVNU8Tpb4obUaSXcRcQ-VMsfQPJm9IzgtRdAY8NN8Xb7PEcYyk
   lBjvTtuPbpzIaqyiUepzUXNDFuAOOkrIol3WmflPUUgMKULBN0EUd1fpOD70p
   RM0rlp_gg_WNUKoW1V-3keYUJoXH9NztEDm_D2MQXj9eGOJJ8yPgGL8PAZMLe
   2R7jb9TxOCPDED7tY_TU4nFPlxptw59A42mldEmViXsKQt60s1SLboazxFKve
   qXC_jpLUt22OC6GUG63p-REw-ZOr3r845z50wMuzifQrMI9bQ",
         "kty": "RSA"
      }]},
      "example_extension_parameter": "example_value"
     }

3.1.1.  Client Registration Request Using a Software Statement

   In addition to JSON elements, client metadata values MAY also be
   provided in a software statement, as described in Section 2.3.  The
   authorization server MAY ignore the software statement if it does not
   support this feature.  If the server supports software statements,
   client metadata values conveyed in the software statement MUST take
   precedence over those conveyed using plain JSON elements.

   Software statements are included in the requesting JSON object using
   this OPTIONAL member:

   software_statement
      A software statement containing client metadata values about the
      client software as claims.  This is a string value containing the
      entire signed JWT.




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   In the following example, some registration parameters are conveyed
   as claims in a software statement from the example in Section 2.3,
   while some values specific to the client instance are conveyed as
   regular parameters (with line breaks within values for display
   purposes only):

     POST /register HTTP/1.1
     Content-Type: application/json
     Accept: application/json
     Host: server.example.com

     {
       "redirect_uris": [
         "https://client.example.org/callback",
         "https://client.example.org/callback2"
       ],
       "software_statement": "eyJhbGciOiJSUzI1NiJ9.
   eyJzb2Z0d2FyZV9pZCI6IjROUkIxLTBYWkFCWkk5RTYtNVNNM1IiLCJjbGll
   bnRfbmFtZSI6IkV4YW1wbGUgU3RhdGVtZW50LWJhc2VkIENsaWVudCIsImNs
   aWVudF91cmkiOiJodHRwczovL2NsaWVudC5leGFtcGxlLm5ldC8ifQ.
   GHfL4QNIrQwL18BSRdE595T9jbzqa06R9BT8w409x9oIcKaZo_mt15riEXHa
   zdISUvDIZhtiyNrSHQ8K4TvqWxH6uJgcmoodZdPwmWRIEYbQDLqPNxREtYn0
   5X3AR7ia4FRjQ2ojZjk5fJqJdQ-JcfxyhK-P8BAWBd6I2LLA77IG32xtbhxY
   fHX7VhuU5ProJO8uvu3Ayv4XRhLZJY4yKfmyjiiKiPNe-Ia4SMy_d_QSWxsk
   U5XIQl5Sa2YRPMbDRXttm2TfnZM1xx70DoYi8g6czz-CPGRi4SW_S2RKHIJf
   IjoI3zTJ0Y2oe0_EJAiXbL6OyF9S5tKxDXV8JIndSA",
       "scope": "read write",
       "example_extension_parameter": "example_value"
     }

3.2.  Responses

   Upon a successful registration request, the authorization server
   returns a client identifier for the client.  The server responds with
   an HTTP 201 Created status code and a body of type "application/json"
   with content as described in Section 3.2.1.

   Upon an unsuccessful registration request, the authorization server
   responds with an error, as described in Section 3.2.2.

3.2.1.  Client Information Response

   The response contains the client identifier as well as the client
   secret, if the client is a confidential client.  The response MAY
   contain additional fields as specified by extensions to this
   specification.





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   client_id
      REQUIRED.  OAuth 2.0 client identifier string.  It SHOULD NOT be
      currently valid for any other registered client, though an
      authorization server MAY issue the same client identifier to
      multiple instances of a registered client at its discretion.

   client_secret
      OPTIONAL.  OAuth 2.0 client secret string.  If issued, this MUST
      be unique for each "client_id" and SHOULD be unique for multiple
      instances of a client using the same "client_id".  This value is
      used by confidential clients to authenticate to the token
      endpoint, as described in OAuth 2.0 [RFC6749], Section 2.3.1.

   client_id_issued_at
      OPTIONAL.  Time at which the client identifier was issued.  The
      time is represented as the number of seconds from
      1970-01-01T00:00:00Z as measured in UTC until the date/time of
      issuance.

   client_secret_expires_at
      REQUIRED if "client_secret" is issued.  Time at which the client
      secret will expire or 0 if it will not expire.  The time is
      represented as the number of seconds from 1970-01-01T00:00:00Z as
      measured in UTC until the date/time of expiration.

   Additionally, the authorization server MUST return all registered
   metadata about this client, including any fields provisioned by the
   authorization server itself.  The authorization server MAY reject or
   replace any of the client's requested metadata values submitted
   during the registration and substitute them with suitable values.
   The client or developer can check the values in the response to
   determine if the registration is sufficient for use (e.g., the
   registered "token_endpoint_auth_method" is supported by the client
   software) and determine a course of action appropriate for the client
   software.  The response to such a situation is out of scope for this
   specification but could include filing a report with the application
   developer or authorization server provider, attempted re-registration
   with different metadata values, or various other methods.  For
   instance, if the server also supports a registration management
   mechanism such as that defined in [RFC7592], the client or developer
   could attempt to update the registration with different metadata
   values.  This process could also be aided by a service discovery
   protocol, such as [OpenID.Discovery], which can list a server's
   capabilities, allowing a client to make a more informed registration
   request.  The use of any such management or discovery system is
   optional and outside the scope of this specification.





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   The successful registration response uses an HTTP 201 Created status
   code with a body of type "application/json" consisting of a single
   JSON object [RFC7159] with all parameters as top-level members of the
   object.

   If a software statement was used as part of the registration, its
   value MUST be returned unmodified in the response along with other
   metadata using the "software_statement" member name.  Client metadata
   elements used from the software statement MUST also be returned
   directly as top-level client metadata values in the registration
   response (possibly with different values, since the values requested
   and the values used may differ).

   The following is a non-normative example response of a successful
   registration:

     HTTP/1.1 201 Created
     Content-Type: application/json
     Cache-Control: no-store
     Pragma: no-cache

     {
      "client_id": "s6BhdRkqt3",
      "client_secret": "cf136dc3c1fc93f31185e5885805d",
      "client_id_issued_at": 2893256800,
      "client_secret_expires_at": 2893276800,
      "redirect_uris": [
        "https://client.example.org/callback",
        "https://client.example.org/callback2"],
      "grant_types": ["authorization_code", "refresh_token"],
      "client_name": "My Example Client",
      "client_name#ja-Jpan-JP":
         "\u30AF\u30E9\u30A4\u30A2\u30F3\u30C8\u540D",
      "token_endpoint_auth_method": "client_secret_basic",
      "logo_uri": "https://client.example.org/logo.png",
      "jwks_uri": "https://client.example.org/my_public_keys.jwks",
      "example_extension_parameter": "example_value"
     }

3.2.2.  Client Registration Error Response

   When an OAuth 2.0 error condition occurs, such as the client
   presenting an invalid initial access token, the authorization server
   returns an error response appropriate to the OAuth 2.0 token type.







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   When a registration error condition occurs, the authorization server
   returns an HTTP 400 status code (unless otherwise specified) with
   content type "application/json" consisting of a JSON object [RFC7159]
   describing the error in the response body.

   Two members are defined for inclusion in the JSON object:

   error
      REQUIRED.  Single ASCII error code string.

   error_description
      OPTIONAL.  Human-readable ASCII text description of the error used
      for debugging.

   Other members MAY also be included and, if they are not understood,
   they MUST be ignored.

   This specification defines the following error codes:

   invalid_redirect_uri
      The value of one or more redirection URIs is invalid.

   invalid_client_metadata
      The value of one of the client metadata fields is invalid and the
      server has rejected this request.  Note that an authorization
      server MAY choose to substitute a valid value for any requested
      parameter of a client's metadata.

   invalid_software_statement
      The software statement presented is invalid.

   unapproved_software_statement
      The software statement presented is not approved for use by this
      authorization server.

















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   The following is a non-normative example of an error response
   resulting from a redirection URI that has been blacklisted by the
   authorization server (with line breaks within values for display
   purposes only):

     HTTP/1.1 400 Bad Request
     Content-Type: application/json
     Cache-Control: no-store
     Pragma: no-cache

     {
      "error": "invalid_redirect_uri",
      "error_description": "The redirection URI
        http://sketchy.example.com is not allowed by this server."
     }

   The following is a non-normative example of an error response
   resulting from an inconsistent combination of "response_types" and
   "grant_types" values (with line breaks within values for display
   purposes only):

     HTTP/1.1 400 Bad Request
     Content-Type: application/json
     Cache-Control: no-store
     Pragma: no-cache

     {
      "error": "invalid_client_metadata",
      "error_description": "The grant type 'authorization_code' must be
        registered along with the response type 'code' but found only
       'implicit' instead."
     }

4.  IANA Considerations

4.1.  OAuth Dynamic Client Registration Metadata Registry

   This specification establishes the "OAuth Dynamic Client Registration
   Metadata" registry.

   OAuth registration client metadata names and descriptions are
   registered with a Specification Required ([RFC5226]) 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 names prior to publication, the Designated Experts may
   approve registration once they are satisfied that such a
   specification will be published, per [RFC7120].




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   Registration requests sent to the mailing list for review should use
   an appropriate subject (e.g., "Request to register OAuth Dynamic
   Client Registration Metadata name: 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.

   IANA must only accept registry updates from the Designated Experts
   and should direct all requests for registration to the review mailing
   list.

4.1.1.  Registration Template

   Client Metadata Name:
      The name requested (e.g., "example").  This name is case
      sensitive.  Names that match other registered names in a case-
      insensitive manner SHOULD NOT be accepted.

   Client Metadata Description:
      Brief description of the metadata value (e.g., "Example
      description").

   Change Controller:
      For Standards Track RFCs, list "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 client
      metadata definition, preferably including a URI that can be used
      to retrieve a copy of the documents.  An indication of the
      relevant sections may also be included but is not required.

4.1.2.  Initial Registry Contents

   The initial contents of the "OAuth Dynamic Client Registration
   Metadata" registry are:

   o  Client Metadata Name: "redirect_uris"
   o  Client Metadata Description: Array of redirection URIs for use in
      redirect-based flows
   o  Change Controller: IESG
   o  Specification Document(s): RFC 7591






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   o  Client Metadata Name: "token_endpoint_auth_method"
   o  Client Metadata Description: Requested authentication method for
      the token endpoint
   o  Change Controller: IESG
   o  Specification Document(s): RFC 7591

   o  Client Metadata Name: "grant_types"
   o  Client Metadata Description: Array of OAuth 2.0 grant types that
      the client may use
   o  Change Controller: IESG
   o  Specification Document(s): RFC 7591

   o  Client Metadata Name: "response_types"
   o  Client Metadata Description: Array of the OAuth 2.0 response types
      that the client may use
   o  Change Controller: IESG
   o  Specification Document(s): RFC 7591

   o  Client Metadata Name: "client_name"
   o  Client Metadata Description: Human-readable name of the client to
      be presented to the user
   o  Change Controller: IESG
   o  Specification Document(s): RFC 7591

   o  Client Metadata Name: "client_uri"
   o  Client Metadata Description: URL of a web page providing
      information about the client
   o  Change Controller: IESG
   o  Specification Document(s): RFC 7591

   o  Client Metadata Name: "logo_uri"
   o  Client Metadata Description: URL that references a logo for the
      client
   o  Change Controller: IESG
   o  Specification Document(s): RFC 7591

   o  Client Metadata Name: "scope"
   o  Client Metadata Description: Space-separated list of OAuth 2.0
      scope values
   o  Change Controller: IESG
   o  Specification Document(s): RFC 7591










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   o  Client Metadata Name: "contacts"
   o  Client Metadata Description: Array of strings representing ways to
      contact people responsible for this client, typically email
      addresses
   o  Change Controller: IESG
   o  Specification Document(s): RFC 7591

   o  Client Metadata Name: "tos_uri"
   o  Client Metadata Description: URL that points to a human-readable
      terms of service document for the client
   o  Change Controller: IESG
   o  Specification Document(s): RFC 7591

   o  Client Metadata Name: "policy_uri"
   o  Client Metadata Description: URL that points to a human-readable
      policy document for the client
   o  Change Controller: IESG
   o  Specification Document(s): RFC 7591

   o  Client Metadata Name: "jwks_uri"
   o  Client Metadata Description: URL referencing the client's JSON Web
      Key Set [RFC7517] document representing the client's public keys
   o  Change Controller: IESG
   o  Specification Document(s): RFC 7591

   o  Client Metadata Name: "jwks"
   o  Client Metadata Description: Client's JSON Web Key Set [RFC7517]
      document representing the client's public keys
   o  Change Controller: IESG
   o  Specification Document(s): RFC 7591

   o  Client Metadata Name: "software_id"
   o  Client Metadata Description: Identifier for the software that
      comprises a client
   o  Change Controller: IESG
   o  Specification Document(s): RFC 7591

   o  Client Metadata Name: "software_version"
   o  Client Metadata Description: Version identifier for the software
      that comprises a client
   o  Change Controller: IESG
   o  Specification Document(s): RFC 7591

   o  Client Metadata Name: "client_id"
   o  Client Metadata Description: Client identifier
   o  Change Controller: IESG
   o  Specification Document(s): RFC 7591




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   o  Client Metadata Name: "client_secret"
   o  Client Metadata Description: Client secret
   o  Change Controller: IESG
   o  Specification Document(s): RFC 7591

   o  Client Metadata Name: "client_id_issued_at"
   o  Client Metadata Description: Time at which the client identifier
      was issued
   o  Change Controller: IESG
   o  Specification Document(s): RFC 7591

   o  Client Metadata Name: "client_secret_expires_at"
   o  Client Metadata Description: Time at which the client secret will
      expire
   o  Change Controller: IESG
   o  Specification Document(s): RFC 7591

4.2.  OAuth Token Endpoint Authentication Methods Registry

   This specification establishes the "OAuth Token Endpoint
   Authentication Methods" registry.

   Additional values for use as "token_endpoint_auth_method" values are
   registered with a Specification Required ([RFC5226]) 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, per [RFC7120].

   Registration requests must be sent to the oauth-ext-review@ietf.org
   mailing list for review and comment, with an appropriate subject
   (e.g., "Request to register token_endpoint_auth_method value:
   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.

   IANA must only accept registry updates from the Designated Experts
   and should direct all requests for registration to the review mailing
   list.








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4.2.1.  Registration Template

   Token Endpoint Authentication Method Name:
      The name requested (e.g., "example").  This name is case
      sensitive.  Names that match other registered names in a case-
      insensitive manner SHOULD NOT be accepted.

   Change Controller:
      For Standards Track RFCs, list "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 token
      endpoint authentication method, preferably including a URI that
      can be used to retrieve a copy of the document or documents.  An
      indication of the relevant sections may also be included but is
      not required.

4.2.2.  Initial Registry Contents

   The initial contents of the "OAuth Token Endpoint Authentication
   Methods" registry are:

   o  Token Endpoint Authentication Method Name: "none"
   o  Change Controller: IESG
   o  Specification Document(s): RFC 7591

   o  Token Endpoint Authentication Method Name: "client_secret_post"
   o  Change Controller: IESG
   o  Specification Document(s): RFC 7591

   o  Token Endpoint Authentication Method Name: "client_secret_basic"
   o  Change Controller: IESG
   o  Specification Document(s): RFC 7591

5.  Security Considerations

   Since requests to the client registration endpoint result in the
   transmission of clear-text credentials (in the HTTP request and
   response), the authorization server MUST require the use of a
   transport-layer security mechanism when sending requests to the
   registration endpoint.  The server MUST support TLS 1.2 [RFC5246] and
   MAY support additional transport-layer security 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 TLS and DTLS [BCP195].



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   For clients that use redirect-based grant types such as
   "authorization_code" and "implicit", authorization servers MUST
   require clients to register their redirection URI values.  This can
   help mitigate attacks where rogue actors inject and impersonate a
   validly registered client and intercept its authorization code or
   tokens through an invalid redirection URI or open redirector.
   Additionally, in order to prevent hijacking of the return values of
   the redirection, registered redirection URI values MUST be one of:

   o  A remote web site protected by TLS
      (e.g., https://client.example.com/oauth_redirect)
   o  A web site hosted on the local machine using an HTTP URI
      (e.g., http://localhost:8080/oauth_redirect)
   o  A non-HTTP application-specific URL that is available only to the
      client application
      (e.g., exampleapp://oauth_redirect)

   Public clients MAY register with an authorization server using this
   protocol, if the authorization server's policy allows them.  Public
   clients use a "none" value for the "token_endpoint_auth_method"
   metadata field and are generally used with the "implicit" grant type.
   Often these clients will be short-lived in-browser applications
   requesting access to a user's resources and access is tied to a
   user's active session at the authorization server.  Since such
   clients often do not have long-term storage, it is possible that such
   clients would need to re-register every time the browser application
   is loaded.  To avoid the resulting proliferation of dead client
   identifiers, an authorization server MAY decide to expire
   registrations for existing clients meeting certain criteria after a
   period of time has elapsed.  Alternatively, such clients could be
   registered on the server where the in-browser application's code is
   served from, and the client's configuration could be pushed to the
   browser alongside the code.

   Since different OAuth 2.0 grant types have different security and
   usage properties, an authorization server MAY require separate
   registrations for a piece of software to support multiple grant
   types.  For instance, an authorization server might require that all
   clients using the "authorization_code" grant type make use of a
   client secret for the "token_endpoint_auth_method" but any clients
   using the "implicit" grant type not use any authentication at the
   token endpoint.  In such a situation, a server MAY disallow clients
   from registering for both the "authorization_code" and "implicit"
   grant types simultaneously.  Similarly, the "authorization_code"
   grant type is used to represent access on behalf of an end-user, but
   the "client_credentials" grant type represents access on behalf of
   the client itself.  For security reasons, an authorization server
   could require that different scopes be used for these different use



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   cases, and, as a consequence, it MAY disallow these two grant types
   from being registered together by the same client.  In all of these
   cases, the authorization server would respond with an
   "invalid_client_metadata" error response.

   Unless used as a claim in a software statement, the authorization
   server MUST treat all client metadata as self-asserted.  For
   instance, a rogue client might use the name and logo of a legitimate
   client that it is trying to impersonate.  Additionally, a rogue
   client might try to use the software identifier or software version
   of a legitimate client to attempt to associate itself on the
   authorization server with instances of the legitimate client.  To
   counteract this, an authorization server MUST take appropriate steps
   to mitigate this risk by looking at the entire registration request
   and client configuration.  For instance, an authorization server
   could issue a warning if the domain/site of the logo doesn't match
   the domain/site of redirection URIs.  An authorization server could
   also refuse registration requests from a known software identifier
   that is requesting different redirection URIs or a different client
   URI.  An authorization server can also present warning messages to
   end-users about dynamically registered clients in all cases,
   especially if such clients have been recently registered or have not
   been trusted by any users at the authorization server before.

   In a situation where the authorization server is supporting open
   client registration, it must be extremely careful with any URL
   provided by the client that will be displayed to the user (e.g.,
   "logo_uri", "tos_uri", "client_uri", and "policy_uri").  For
   instance, a rogue client could specify a registration request with a
   reference to a drive-by download in the "policy_uri", enticing the
   user to click on it during the authorization.  The authorization
   server SHOULD check to see if the "logo_uri", "tos_uri",
   "client_uri", and "policy_uri" have the same host and scheme as the
   those defined in the array of "redirect_uris" and that all of these
   URIs resolve to valid web pages.  Since these URI values that are
   intended to be displayed to the user at the authorization page, the
   authorization server SHOULD protect the user from malicious content
   hosted at the URLs where possible.  For instance, before presenting
   the URLs to the user at the authorization page, the authorization
   server could download the content hosted at the URLs, check the
   content against a malware scanner and blacklist filter, determine
   whether or not there is mixed secure and non-secure content at the
   URL, and other possible server-side mitigations.  Note that the
   content in these URLs can change at any time and the authorization
   server cannot provide complete confidence in the safety of the URLs,
   but these practices could help.  To further mitigate this kind of
   threat, the authorization server can also warn the user that the URL
   links have been provided by a third party, should be treated with



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   caution, and are not hosted by the authorization server itself.  For
   instance, instead of providing the links directly in an HTML anchor,
   the authorization server can direct the user to an interstitial
   warning page before allowing the user to continue to the target URL.

   Clients MAY use both the direct JSON object and the JWT-encoded
   software statement to present client metadata to the authorization
   server as part of the registration request.  A software statement is
   cryptographically protected and represents claims made by the issuer
   of the statement, while the JSON object represents the self-asserted
   claims made by the client or developer directly.  If the software
   statement is valid and signed by an acceptable authority (such as the
   software API publisher), the values of client metadata within the
   software statement MUST take precedence over those metadata values
   presented in the plain JSON object, which could have been intercepted
   and modified.

   Like all metadata values, the software statement is an item that is
   self-asserted by the client, even though its contents have been
   digitally signed or MACed by the issuer of the software statement.
   As such, presentation of the software statement is not sufficient in
   most cases to fully identify a piece of client software.  An initial
   access token, in contrast, does not necessarily contain information
   about a particular piece of client software but instead represents
   authorization to use the registration endpoint.  An authorization
   server MUST consider the full registration request, including the
   software statement, initial access token, and JSON client metadata
   values, when deciding whether to honor a given registration request.

   If an authorization server receives a registration request for a
   client that is not intended to have multiple instances registered
   simultaneously and the authorization server can infer a duplication
   of registration (e.g., it uses the same "software_id" and
   "software_version" values as another existing client), the server
   SHOULD treat the new registration as being suspect and reject the
   registration.  It is possible that the new client is trying to
   impersonate the existing client in order to trick users into
   authorizing it, or that the original registration is no longer valid.
   The details of managing this situation are specific to the
   authorization server deployment and outside the scope of this
   specification.

   Since a client identifier is a public value that can be used to
   impersonate a client at the authorization endpoint, an authorization
   server that decides to issue the same client identifier to multiple
   instances of a registered client needs to be very particular about
   the circumstances under which this occurs.  For instance, the
   authorization server can limit a given client identifier to clients



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   using the same redirect-based flow and the same redirection URIs.  An
   authorization server SHOULD NOT issue the same client secret to
   multiple instances of a registered client, even if they are issued
   the same client identifier, or else the client secret could be
   leaked, allowing malicious impostors to impersonate a confidential
   client.

6.  Privacy Considerations

   As the protocol described in this specification deals almost
   exclusively with information about software and not people, there are
   very few privacy concerns for its use.  The notable exception is the
   "contacts" field as defined in Section 2, which contains contact
   information for the developers or other parties responsible for the
   client software.  These values are intended to be displayed to end-
   users and will be available to the administrators of the
   authorization server.  As such, the developer may wish to provide an
   email address or other contact information expressly dedicated to the
   purpose of supporting the client instead of using their personal or
   professional addresses.  Alternatively, the developer may wish to
   provide a collective email address for the client to allow for
   continuing contact and support of the client software after the
   developer moves on and someone else takes over that responsibility.

   In general, the metadata for a client, such as the client name and
   software identifier, are common across all instances of a piece of
   client software and therefore pose no privacy issues for end-users.
   Client identifiers, on the other hand, are often unique to a specific
   instance of a client.  For clients such as web sites that are used by
   many users, there may not be significant privacy concerns regarding
   the client identifier, but for clients such as native applications
   that are installed on a single end-user's device, the client
   identifier could be uniquely tracked during OAuth 2.0 transactions
   and its use tied to that single end-user.  However, as the client
   software still needs to be authorized by a resource owner through an
   OAuth 2.0 authorization grant, this type of tracking can occur
   whether or not the client identifier is unique by correlating the
   authenticated resource owner with the requesting client identifier.

   Note that clients are forbidden by this specification from creating
   their own client identifier.  If the client were able to do so, an
   individual client instance could be tracked across multiple colluding
   authorization servers, leading to privacy and security issues.
   Additionally, client identifiers are generally issued uniquely per
   registration request, even for the same instance of software.  In
   this way, an application could marginally improve privacy by
   registering multiple times and appearing to be completely separate




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   applications.  However, this technique does incur significant
   usability cost in the form of requiring multiple authorizations per
   resource owner and is therefore unlikely to be used in practice.

7.  References

7.1.  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.Language]
              IANA, "Language Subtag Registry",
              <http://www.iana.org/assignments/
              language-subtag-registry>.

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

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              DOI 10.17487/RFC5226, May 2008,
              <http://www.rfc-editor.org/info/rfc5226>.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <http://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, <http://www.rfc-editor.org/info/rfc5646>.

   [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, <http://www.rfc-editor.org/info/rfc6125>.

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



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

   [RFC7120]  Cotton, M., "Early IANA Allocation of Standards Track Code
              Points", BCP 100, RFC 7120, DOI 10.17487/RFC7120, January
              2014, <http://www.rfc-editor.org/info/rfc7120>.

   [RFC7159]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
              2014, <http://www.rfc-editor.org/info/rfc7159>.

   [RFC7515]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web
              Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
              2015, <http://www.rfc-editor.org/info/rfc7515>.

   [RFC7517]  Jones, M., "JSON Web Key (JWK)", RFC 7517,
              DOI 10.17487/RFC7517, May 2015,
              <http://www.rfc-editor.org/info/rfc7517>.

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

   [RFC7522]  Campbell, B., Mortimore, C., and M. Jones, "Security
              Assertion Markup Language (SAML) 2.0 Profile for OAuth 2.0
              Client Authentication and Authorization Grants", RFC 7522,
              DOI 10.17487/RFC7522, May 2015,
              <http://www.rfc-editor.org/info/rfc7522>.

   [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, <http://www.rfc-editor.org/info/rfc7523>.
















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7.2.  Informative References

   [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>.

   [RFC7592]  Richer, J., Jones, M., Bradley, J., and M. Machulak,
              "OAuth 2.0 Dynamic Client Registration Management
              Protocol", RFC 7592, DOI 10.17487/RFC7592, July 2015,
              <http://www.rfc-editor.org/info/rfc7592>.

   [UMA-Core]
              Hardjono, T., Maler, E., Machulak, M., and D. Catalano,
              "User-Managed Access (UMA) Profile of OAuth 2.0", Work in
              Progress, draft-hardjono-oauth-umacore-13, April 2015.




























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Appendix A.  Use Cases

   This appendix describes different ways that this specification can be
   utilized, including describing some of the choices that may need to
   be made.  Some of the choices are independent and can be used in
   combination, whereas some of the choices are interrelated.

A.1.  Open versus Protected Dynamic Client Registration

A.1.1.  Open Dynamic Client Registration

   Authorization servers that support open registration allow
   registrations to be made with no initial access token.  This allows
   all client software to register with the authorization server.

A.1.2.  Protected Dynamic Client Registration

   Authorization servers that support protected registration require
   that an initial access token be used when making registration
   requests.  While the method by which a client or developer receives
   this initial access token and the method by which the authorization
   server validates this initial access token are out of scope for this
   specification, a common approach is for the developer to use a manual
   preregistration portal at the authorization server that issues an
   initial access token to the developer.

A.2.  Registration without or with Software Statements

A.2.1.  Registration without a Software Statement

   When a software statement is not used in the registration request,
   the authorization server must be willing to use client metadata
   values without them being digitally signed or MACed (and thereby
   attested to) by any authority.  (Note that this choice is independent
   of the Open versus Protected choice, and that an initial access token
   is another possible form of attestation.)

A.2.2.  Registration with a Software Statement

   A software statement can be used in a registration request to provide
   attestation by an authority for a set of client metadata values.
   This can be useful when the authorization server wants to restrict
   registration to client software attested to by a set of authorities
   or when it wants to know that multiple registration requests refer to
   the same piece of client software.






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A.3.  Registration by the Client or Developer

A.3.1.  Registration by the Client

   In some use cases, client software will dynamically register itself
   with an authorization server to obtain a client identifier and other
   information needed to interact with the authorization server.  In
   this case, no client identifier for the authorization server is
   packaged with the client software.

A.3.2.  Registration by the Developer

   In some cases, the developer (or development software being used by
   the developer) will preregister the client software with the
   authorization server or a set of authorization servers.  In this
   case, the client identifier value(s) for the authorization server(s)
   can be packaged with the client software.

A.4.  Client ID per Client Instance or per Client Software

A.4.1.  Client ID per Client Software Instance

   In some cases, each deployed instance of a piece of client software
   will dynamically register and obtain distinct client identifier
   values.  This can be advantageous, for instance, if the code flow is
   being used, as it also enables each client instance to have its own
   client secret.  This can be useful for native clients, which cannot
   maintain the secrecy of a client secret value packaged with the
   software, but which may be able to maintain the secrecy of a per-
   instance client secret.

A.4.2.  Client ID Shared among All Instances of Client Software

   In some cases, each deployed instance of a piece of client software
   will share a common client identifier value.  For instance, this is
   often the case for in-browser clients using the implicit flow, when
   no client secret is involved.  Particular authorization servers might
   choose, for instance, to maintain a mapping between software
   statement values and client identifier values, and return the same
   client identifier value for all registration requests for a
   particular piece of software.  The circumstances under which an
   authorization server would do so, and the specific software statement
   characteristics required in this case, are beyond the scope of this
   specification.







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A.5.  Stateful or Stateless Registration

A.5.1.  Stateful Client Registration

   In some cases, authorization servers will maintain state about
   registered clients, typically indexing this state using the client
   identifier value.  This state would typically include the client
   metadata values associated with the client registration, and possibly
   other state specific to the authorization server's implementation.
   When stateful registration is used, operations to support retrieving
   and/or updating this state may be supported.  One possible set of
   operations upon stateful registrations is described in [RFC7592].

A.5.2.  Stateless Client Registration

   In some cases, authorization servers will be implemented in a manner
   the enables them to not maintain any local state about registered
   clients.  One means of doing this is to encode all the registration
   state in the returned client identifier value, and possibly
   encrypting the state to the authorization server to maintain the
   confidentiality and integrity of the state.

Acknowledgments

   The authors thank the OAuth Working Group, the User-Managed Access
   Working Group, and the OpenID Connect Working Group participants for
   their input to this document.  In particular, the following
   individuals have been instrumental in their review and contribution
   to various draft versions of this document: Amanda Anganes, Derek
   Atkins, Tim Bray, Domenico Catalano, Donald Coffin, Vladimir
   Dzhuvinov, George Fletcher, Thomas Hardjono, William Kim, Torsten
   Lodderstedt, Eve Maler, Josh Mandel, Nov Matake, Tony Nadalin, Nat
   Sakimura, Christian Scholz, and Hannes Tschofenig.


















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Authors' Addresses

   Justin Richer (editor)

   Email: ietf@justin.richer.org


   Michael B. Jones
   Microsoft

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


   John Bradley
   Ping Identity

   Email: ve7jtb@ve7jtb.com


   Maciej Machulak
   Newcastle University

   Email: maciej.machulak@gmail.com


   Phil Hunt
   Oracle Corporation

   Email: phil.hunt@yahoo.com





















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