OAuth Working Group J. Richer
Internet-Draft The MITRE Corporation
Intended status: Standards Track M. Jones
Expires: February 6, 2015 Microsoft
J. Bradley
Ping Identity
M. Machulak
Newcastle University
P. Hunt
Oracle Corporation
August 5, 2014

OAuth 2.0 Dynamic Client Registration Protocol
draft-ietf-oauth-dyn-reg-19

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 and 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 Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at http://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on February 6, 2015.

Copyright Notice

Copyright (c) 2014 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.


Table of Contents

1. Introduction

In order for an OAuth 2.0 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 MACed; 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 specficiation generalizes the registration mechanisms defined by the OpenID Connect Dynamic Client Registration 1.0 [OpenID.Registration] specification and used by the User Managed Access (UMA) Profile of OAuth 2.0 [I-D.hardjono-oauth-umacore] specification 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", "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) [JWT].

This specification defines the following terms:

Client Developer

The person or organization that builds a client software package and prepares it for distribution.
Client Instance

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

Software implementing an OAuth 2.0 client.
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 is deployed and protected by an OAuth 2.0 framework. In simple cloud deployments, the software API publisher and the deployment organization may be the same. In other scenarios, a software publisher may be working with many different deployment organizations.
Software API Deployment

A deployed instance of a software API that is protected by OAuth 2.0 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 deployed in one or more deployment environments. A publisher may be any commercial, public, private, or open source organization that is responsible for publishing and distributing software that may be protected via OAuth 2.0. In some cases a software API publisher and a client developer may be the same organization.
Software Statement

Digitally signed or MACed JSON Web Token (JWT) [JWT] that asserts metadata values about the client software. In some cases, a software statement will be issued directly by the organization or developer that creates the client software. In other cases, a software statement will be issued by a third party organization for use by the organization or developer that creates the client software. 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.

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    |
 |           |                                      +---------------+
 +-----------+

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, a set of client credentials such as a client secret if applicable for this client, and possibly other values.

2. Client Metadata

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.

The client metadata values are used in two ways:

The following client metadata fields are defined by this specification. The implementation and use of all client metadata fields is OPTIONAL, unless stated otherwise.

redirect_uris

Array of redirection URI values 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

The requested authentication method for the token endpoint. Values defined by this specification are:

Additional values can be defined via the IANA OAuth Token Endpoint Authentication Methods Registry established in

Section 5.2. 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 HTTP Basic Authentication Scheme as specified in Section 2.3.1 of OAuth 2.0.
grant_types

Array of OAuth 2.0 grant types that the client may use. These grant types are defined as follows:

Authorization Servers MAY allow for other values as defined in grant type extensions to OAuth 2.0. The extension process is described in OAuth 2.0 Section 2.5. 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 extension. If omitted, the default is that the client will use only the authorization_code Grant Type.
response_types

Array of the OAuth 2.0 response types that the client may use. These response types are defined as follows:

Authorization servers MAY allow for other values as defined in response type extensions to OAuth 2.0. The extension process is described in OAuth 2.0 Section 2.5. 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 extension. If omitted, the default is that the client will use only the code response type.
client_name

Human-readable name of the client to be presented to the user during authorization. If omitted, the authorization server MAY display the raw client_id value to the 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 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 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

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 is 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 addresses available to end users for support requests for the client.
tos_uri

URL 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 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 referencing the client's JSON Web Key Set [JWK] 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 [OAuth.JWT]. 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 be used together.
jwks

Client's JSON Web Key Set [JWK] 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 be used together.
software_id

Identifier for the software that comprises a client. Unlike client_id, which is issued by the authorization server and may vary between instances, the software_id is asserted by the client software on behalf of the software developer and is intended to be shared among all instances of the client software. The identifier SHOULD NOT change when software version changes or when a new installation occurs.
software_version

Version identifier for the software that comprises a client. The value of this field is a string that is intended to be compared using string equality matching. The value of the software_version SHOULD change on any update to the client software.

Extensions and profiles of this specification MAY expand this list. The authorization server MUST ignore any client metadata values sent by the client that it does not understand.

Client metadata values can either be 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, or a mixture of both. 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 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, BCP47 [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 BCP47 language tag values are case insensitive, implementations SHOULD interpret the language tag values supplied in a case insensitive manner. Per the recommendations in BCP47, 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.

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 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) [JWT] 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 JWS [JWS] 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.

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 registering with a software API publisher to obtain a software statement for a class of clients. The software statement is typically distributed with all instances of a client application.

The criteria by which authorization servers determine whether to trust and utilize the information in a software statement are beyond 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 beyond 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 entity body using the application/json format. The client registration endpoint MUST be protected by a transport-layer security mechanism, and the server MUST support TLS 1.2 RFC 5246 [RFC5246] and/or TLS 1.0 [RFC2246] and MAY support additional transport-layer mechanisms meeting its security requirements. When using TLS, the client MUST perform a TLS/SSL server certificate check, per RFC 6125 [RFC6125].

The client registration endpoint MAY be an OAuth 2.0 protected resource and accept an initial access token in the form of an OAuth 2.0 [RFC6749] 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.

Client metadata values may also be provided in a software statement, as described in Section 2.3. Software statements are included in the requesting JSON object using this member:

software_statement

A software statement containing client metadata values about the client software as claims.

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:

The following is a non-normative example request not using an initial access token (with line wraps 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"],
   "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.

The following is a non-normative example request using an initial access token (with line wraps 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":[{...omitted for brevity...}]},
   "example_extension_parameter": "example_value"
  }

In the following example, some registration parameters are conveyed as claims in a software statement, while some values specific to the client instance are conveyed as regular parameters (with line wraps 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":"eyJhbGciOiJFUzI1NiJ9.
       eyJpc3Mi[...omitted for brevity...].
       J9l-ZhwP[...omitted for brevity...]",
    "scope":"read write",
    "example_extension_parameter":"example_value"
  }

3.2. Client Registration Response

Upon successful registration, the authorization server returns a client identifier for the client. The server responds with an HTTP 201 Created code and a body of type application/json with content as described in Section 4.1.

Upon an unsuccessful registration, the authorization server responds with an error, as described in Section 4.2.

4. Responses

The following responses are sent in response to registration requests.

4.1. 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.

client_id

REQUIRED. OAuth 2.0 client identifier. 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. If issued, this MUST be unique for each 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 1970-01-01T0:0:0Z as measured in UTC until the date/time.
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 1970-01-01T0:0:0Z as measured in UTC until the date/time.

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 or update requests and substitute them with suitable values.

The response is an application/json document with all parameters as top-level members of a JSON object [RFC7159].

If a software statement was used as part of the registration, its value MUST be returned in the response along with other metadata. 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).

Following is a non-normative example response:

  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"
  }

4.2. 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.

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 not understood, 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.

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 wraps 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."
  }

Following is a non-normative example of an error response resulting from an inconsistent combination of response_types and grant_types values (with line wraps 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."
  }

5. IANA Considerations

5.1. OAuth Dynamic Registration Client Metadata Registry

This specification establishes the OAuth Dynamic Registration Client Metadata registry.

OAuth registration client metadata 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 Expert(s) may approve registration once they are satisfied that such a specification will be published.

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 OAuth Dynamic Registration Client Metadata name: example").

Within the review period, the Designated Expert(s) 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 Expert(s) and should direct all requests for registration to the review mailing list.

5.1.1. 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, state "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(s) that specify the token endpoint authorization method, preferably including a URI that can be used to retrieve a copy of the document(s). An indication of the relevant sections may also be included but is not required.

5.1.2. Initial Registry Contents

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

5.2. 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 metadata 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 Expert(s) may approve registration once they are satisfied that such a specification will be published.

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 Expert(s) 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 Expert(s) and should direct all requests for registration to the review mailing list.

5.2.1. Registration Template

Token Endpoint Authorization 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, state "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(s) that specify the token endpoint authorization method, preferably including a URI that can be used to retrieve a copy of the document(s). An indication of the relevant sections may also be included but is not required.

5.2.2. Initial Registry Contents

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

6. 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 RFC 5246 [RFC5246] and/or TLS 1.0 [RFC2246] and MAY support additional transport-layer mechanisms meeting its security requirements. When using TLS, the client MUST perform a TLS/SSL server certificate check, per RFC 6125 [RFC6125].

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:

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's possible that such clients would need to re-register every time the browser application is loaded. Additionally, such clients may not have ample opportunity to unregister themselves using the delete action before the browser closes. 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.

Since different OAuth 2.0 grant types have different security and usage parameters, 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 do 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 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 needs to take 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 homepage 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. 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.

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 trusted, 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 modified en route.

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 identity 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 uses the same software_id and software_version values as another client, the server should treat the new registration as being suspect. It is possible that the new client is trying to impersonate the existing client.

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 MUST be very particular about the circumstances under which this occurs. For instance, the authorization server can limit a given client identifier to clients 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 imposters to impersonate a confidential client.

7. References

7.1. Normative References

[IANA.Language] Internet Assigned Numbers Authority (IANA), "Language Subtag Registry", 2005.
[JWK] Jones, M., "JSON Web Key (JWK)", Internet-Draft draft-ietf-jose-json-web-key, July 2014.
[JWS] Jones, M., Bradley, J. and N. Sakimura, "JSON Web Signature (JWS)", Internet-Draft draft-ietf-jose-json-web-signature, July 2014.
[JWT] Jones, M., Bradley, J. and N. Sakimura, "JSON Web Token (JWT)", Internet-Draft draft-ietf-oauth-json-web-token, July 2014.
[OAuth.JWT] Jones, M., Campbell, B. and C. Mortimore, "JSON Web Token (JWT) Profile for OAuth 2.0 Client Authentication and Authorization Grants", Internet-Draft draft-ietf-oauth-jwt-bearer, July 2014.
[OAuth.SAML2] Campbell, B., Mortimore, C. and M. Jones, "SAML 2.0 Profile for OAuth 2.0 Client Authentication and Authorization Grants", Internet-Draft draft-ietf-oauth-saml2-bearer, July 2014.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2246] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", RFC 2246, January 1999.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, May 2008.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC5646] Phillips, A. and M. Davis, "Tags for Identifying Languages", BCP 47, RFC 5646, September 2009.
[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, March 2011.
[RFC6749] Hardt, D., "The OAuth 2.0 Authorization Framework", RFC 6749, October 2012.
[RFC6750] Jones, M. and D. Hardt, "The OAuth 2.0 Authorization Framework: Bearer Token Usage", RFC 6750, October 2012.
[RFC7159] Bray, T., "The JavaScript Object Notation (JSON) Data Interchange Format", RFC 7159, March 2014.

7.2. Informative References

[I-D.hardjono-oauth-umacore] Hardjono, T., "User-Managed Access (UMA) Profile of OAuth 2.0", Internet-Draft draft-hardjono-oauth-umacore-10, July 2014.
[OAuth.Registration.Management] Richer, J., Jones, M., Bradley, J., Machulak, M. and P. Hunt, "OAuth 2.0 Dynamic Client Registration Management Protocol", Internet-Draft draft-ietf-oauth-dyn-reg-management, August 2014.
[OpenID.Registration] Sakimura, N., Bradley, J. and M. Jones, "OpenID Connect Dynamic Client Registration 1.0", February 2014.

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 pre-registration 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.

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 pre-register 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.

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 the [OAuth.Registration.Management] specification.

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.

Appendix B. 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 versions of this document: Amanda Anganes, Derek Atkins, Tim Bray, Domenico Catalano, Donald Coffin, Vladimir Dzhuvinov, George Fletcher, Thomas Hardjono, Phil Hunt, William Kim, Torsten Lodderstedt, Eve Maler, Josh Mandel, Nov Matake, Tony Nadalin, Nat Sakimura, Christian Scholz, and Hannes Tschofenig.

Appendix C. Document History

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Authors' Addresses

Justin Richer The MITRE Corporation EMail: jricher@mitre.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: m.p.machulak@ncl.ac.uk URI: http://ncl.ac.uk/
Phil Hunt Oracle Corporation EMail: phil.hunt@yahoo.com