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rfc:rfc7591

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.

Richer, et al. Standards Track [Page 1] RFC 7591 OAuth 2.0 Dynamic Registration July 2015

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.

Richer, et al. Standards Track [Page 2] RFC 7591 OAuth 2.0 Dynamic Registration July 2015

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

Richer, et al. Standards Track [Page 3] RFC 7591 OAuth 2.0 Dynamic Registration July 2015

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",

Richer, et al. Standards Track [Page 4] RFC 7591 OAuth 2.0 Dynamic Registration July 2015

 "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

Richer, et al. Standards Track [Page 5] RFC 7591 OAuth 2.0 Dynamic Registration July 2015

    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.

Richer, et al. Standards Track [Page 6] RFC 7591 OAuth 2.0 Dynamic Registration July 2015

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.

Richer, et al. Standards Track [Page 7] RFC 7591 OAuth 2.0 Dynamic Registration July 2015

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.

Richer, et al. Standards Track [Page 8] RFC 7591 OAuth 2.0 Dynamic Registration July 2015

 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.

Richer, et al. Standards Track [Page 9] RFC 7591 OAuth 2.0 Dynamic Registration July 2015

    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.

Richer, et al. Standards Track [Page 10] RFC 7591 OAuth 2.0 Dynamic Registration July 2015

 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

Richer, et al. Standards Track [Page 11] RFC 7591 OAuth 2.0 Dynamic Registration July 2015

    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

Richer, et al. Standards Track [Page 12] RFC 7591 OAuth 2.0 Dynamic Registration July 2015

 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".

Richer, et al. Standards Track [Page 13] RFC 7591 OAuth 2.0 Dynamic Registration July 2015

 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.

Richer, et al. Standards Track [Page 14] RFC 7591 OAuth 2.0 Dynamic Registration July 2015

 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

Richer, et al. Standards Track [Page 15] RFC 7591 OAuth 2.0 Dynamic Registration July 2015

 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.

Richer, et al. Standards Track [Page 16] RFC 7591 OAuth 2.0 Dynamic Registration July 2015

 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.

Richer, et al. Standards Track [Page 17] RFC 7591 OAuth 2.0 Dynamic Registration July 2015

 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.

Richer, et al. Standards Track [Page 18] RFC 7591 OAuth 2.0 Dynamic Registration July 2015

 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.

Richer, et al. Standards Track [Page 19] RFC 7591 OAuth 2.0 Dynamic Registration July 2015

 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.

Richer, et al. Standards Track [Page 20] RFC 7591 OAuth 2.0 Dynamic Registration July 2015

 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.

Richer, et al. Standards Track [Page 21] RFC 7591 OAuth 2.0 Dynamic Registration July 2015

 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.

Richer, et al. Standards Track [Page 22] RFC 7591 OAuth 2.0 Dynamic Registration July 2015

 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].

Richer, et al. Standards Track [Page 23] RFC 7591 OAuth 2.0 Dynamic Registration July 2015

 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

Richer, et al. Standards Track [Page 24] RFC 7591 OAuth 2.0 Dynamic Registration July 2015

 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

Richer, et al. Standards Track [Page 25] RFC 7591 OAuth 2.0 Dynamic Registration July 2015

 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

Richer, et al. Standards Track [Page 26] RFC 7591 OAuth 2.0 Dynamic Registration July 2015

 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.

Richer, et al. Standards Track [Page 27] RFC 7591 OAuth 2.0 Dynamic Registration July 2015

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].

Richer, et al. Standards Track [Page 28] RFC 7591 OAuth 2.0 Dynamic Registration July 2015

 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

Richer, et al. Standards Track [Page 29] RFC 7591 OAuth 2.0 Dynamic Registration July 2015

 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

Richer, et al. Standards Track [Page 30] RFC 7591 OAuth 2.0 Dynamic Registration July 2015

 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

Richer, et al. Standards Track [Page 31] RFC 7591 OAuth 2.0 Dynamic Registration July 2015

 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

Richer, et al. Standards Track [Page 32] RFC 7591 OAuth 2.0 Dynamic Registration July 2015

 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>.

Richer, et al. Standards Track [Page 33] RFC 7591 OAuth 2.0 Dynamic Registration July 2015

 [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>.

Richer, et al. Standards Track [Page 34] RFC 7591 OAuth 2.0 Dynamic Registration July 2015

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.

Richer, et al. Standards Track [Page 35] RFC 7591 OAuth 2.0 Dynamic Registration July 2015

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.

Richer, et al. Standards Track [Page 36] RFC 7591 OAuth 2.0 Dynamic Registration July 2015

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.

Richer, et al. Standards Track [Page 37] RFC 7591 OAuth 2.0 Dynamic Registration July 2015

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.

Richer, et al. Standards Track [Page 38] RFC 7591 OAuth 2.0 Dynamic Registration July 2015

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

Richer, et al. Standards Track [Page 39]

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