| OAuth Working Group | J. Richer, Ed. |
| Internet-Draft | The MITRE Corporation |
| Intended status: Standards Track | J. Bradley |
| Expires: February 27, 2014 | Ping Identity |
| M.B. Jones | |
| Microsoft | |
| M. Machulak | |
| Newcastle University | |
| August 26, 2013 |
OAuth 2.0 Core Dynamic Client Registration
draft-richer-oauth-dyn-reg-core-00
This specification defines an endpoint and protocol for dynamic registration of OAuth 2.0 clients at an authorization server.
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Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved.
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In some use-case scenarios, it is desirable or necessary to allow OAuth 2.0 clients to obtain authorization from an OAuth 2.0 authorization server without requiring the two parties to interact beforehand. Nevertheless, for the authorization server to accurately and securely represent to end-users which client is seeking authorization to access the end-user's resources, a method for automatic and unique registration of clients is needed. The OAuth 2.0 authorization framework does not define how the relationship between the client and the authorization server is initialized, or how a given client is assigned a unique client identifier. Historically, this has happened out-of-band from the OAuth 2.0 protocol. This draft provides a mechanism for a client to register itself with the authorization server, which can be used to dynamically provision a client identifier, and optionally a client secret. Additionally, the mechanisms in this draft may can be used by a client developer to register the client with the authorization server in a programmatic fashion.
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 redirect URIs.
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.
This specification uses the terms "Access Token", "Refresh Token", "Authorization Code", "Authorization Grant", "Authorization Server", "Authorization Endpoint", "Client", "Client Identifier", "Client Secret", "Protected Resource", "Resource Owner", "Resource Server", and "Token Endpoint" defined by OAuth 2.0 [RFC6749].
This specification defines the following additional terms:
+--------(A)- Initial Access Token
|
v
+-----------+ +---------------+
| |--(B)- Client Registration Request -->| Client |
| Client or | | Registration |
| Developer |<-(C)- Client Information Response ---| Endpoint |
| | +---------------+
+-----------+
Figure 1: Abstract Protocol 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:
Clients generally have an array of metadata associated with their unique client identifier at the authorization server, such as the list of valid redirect URIs.
The client metadata values serve two parallel purposes in the overall OAuth 2.0 dynamic client registration protocol:
An authorization server MAY override any value that a client requests during the registration process (including any omitted values) and replace the requested value with a default at the server's discretion. The authorization server SHOULD provide documentation for any fields that it requires to be filled in by the client or to have particular values or formats. An authorization server MAY ignore the values provided by the client for any field in this list.
Extensions and profiles of this specification MAY expand this list, and authorization servers MUST accept all fields in this list. The authorization server MUST ignore any additional parameters sent by the Client that it does not understand.
Additional values can be defined via the IANA OAuth Token Endpoint Authentication Methods Registry
Section 5.1. 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.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.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.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.
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.
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 registrant 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 initial registration requests with no authorization (which is to say, with no OAuth 2.0 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.
The client registration endpoint MUST ignore all parameters it does not understand.
This operation registers a new client to the authorization server. The authorization server assigns this client a unique client identifier, optionally assigns a client secret, and associates the metadata given in the request with the issued client identifier. The request includes any parameters described in Client Metadata [client-metadata] that the client wishes to specify for itself 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 [RFC4627] document consisting of a JSON object and all parameters 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:
Following is a non-normative example request (with line wraps 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"],
"token_endpoint_auth_method":"client_secret_basic",
"scope":"read write dolphin",
"extension_parameter":"foo"
}
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:
Following is a non-normative example request (with line wraps 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"],
"token_endpoint_auth_method":"client_secret_basic",
"scope":"read write dolphin",
"extension_parameter":"foo"
}
Upon successful registration, the authorization server generates a new client identifier for the client. This client identifier MUST be unique at the server and MUST NOT be in use by any other client. The server responds with an HTTP 201 Created code and a body of type application/json with content described in Client Information Response [client-info-response].
Upon an unsuccessful registration, the authorization server responds with an error as described in Client Registration Error [client-registration-error].
In response to certain requests from the client to either the client registration endpoint as described in this specification, the authorization server sends the following response bodies.
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.
Additionally, the Authorization Server MUST return all registered metadata [client-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 [RFC4627].
Following is a non-normative example response:
HTTP/1.1 200 OK
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"]
"scope": "read write dolphin",
"grant_types": ["authorization_code", "refresh_token"]
"token_endpoint_auth_method": "client_secret_basic",
"extension_parameter": "foo"
}
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 [RFC4627] describing the error in the response body.
The JSON object contains two members:
This specification defines the following error codes:
Following is a non-normative example of an error response (with line wraps 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 redirect URI of http://sketchy.example.com
is not allowed for this server."
}
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.
The OAuth Token Endpoint Authentication Methods registry's initial contents are:
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 SHOULD require clients to register their redirect_uris. Requiring clients to do so can help mitigate attacks where rogue actors inject and impersonate a validly registered client and intercept its authorization code or tokens through an invalid redirect URI.
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 [client-registration-error].
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, Nat Sakimura, Christian Scholz, and Hannes Tschofenig.
[[ Editor's Note: These are some of the collected use cases that this protocol can address, they still need to be refactored into the two specifications. ]]
In the OAuth 2.0 specification [RFC6749], a client is identified by its own unique Client identifier (client_id) at each authorization server that it associates with. Dynamic registration as defined in this document is one way for a client to get a client identifier and associate a set of metadata with that identifier. Lack of such a client identifier is the expected trigger for a client registration operation.
In many cases, this client identifier is a unique, pairwise association between a particular running instance of a piece of client software and a particular running instance of an authorization server software. In particular:
A client identifier (and its associated credentials) could also be shared between multiple instances of a client. Mechanisms for sharing client identifiers between multiple instances of a piece of software (either client or authorization server) are outside the scope of this specification, as it is expected that every successful registration request [RegistrationRequest] results in the issuance of a new client identifier.
There are several patterns of OAuth client registration that dynamic registration protocol can enable. The following non-normative example lifecycle descriptions are not intended to be an exhaustive list. It is assumed that the authorization server supports the dynamic registration protocol and that all necessary discovery steps (which are out of scope for this specification) have already been performed.
Open registration, with no authorization required on the client registration endpoint, works as follows:
Open registration, with no authorization required on the client registration endpoint. The registration endpoint/Authorization server maintain no state for the client. All information is storted in the client_id that is returned to the client and passed back to the Authorization server and Token Endpoint on subsiquent requests. If the client is using the implicit flow then the JWT MUST include the redirect URI and be signed by the AS for its later consumption. If the client is registering it's public key for use in the self signed assertion flow, the JWT MUST include the client's public key in the signed JWT. If the client is using a symetric client secret, the AS MUST include the secret as a claim in the JWT and encrypt or sign and encrypt the token to itself as appropriate. This method is transperent to the client and requires no aditional paramaters.
The flow works as follows:
An authorization server may require an initial access token for requests to its registration endpoint. While the method by which a client 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. This allows the developer to package the initial access token with different instances of the client application. While each copy of the application would get its own client identifier (and registration access token), all instances of the application would be tied back to the developer by their shared use of this initial access token.
The dynamic registration protocol can also be used in place of a manual registration portal, for instance as part of an automated build and deployment process. In this scenario, the authorization server may require an initial access token for requests to its registration endpoint, as described in Protected Registration [ProtectedRegistration]. However, here the developer manages the client's registration instead of the client itself. Therefore, the initial registration token and registration access token all remain with the developer. The developer packages the client identifier with the client as part of the client's build process.
[[ to be removed by the RFC editor before publication as an RFC ]]
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