| Network Working Group | J. Richer, Ed. |
| Internet-Draft | The MITRE Corporation |
| Intended status: Standards Track | J. Bradley |
| Expires: July 12, 2013 | Ping Identity |
| M.B. Jones | |
| Microsoft | |
| M. Machulak | |
| Newcastle University | |
| January 08, 2013 |
OAuth Dynamic Client Registration Protocol
draft-ietf-oauth-dyn-reg-04
This specification defines an endpoint and protocol for dynamic registration of OAuth Clients at an Authorization Server.
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on July 12, 2013.
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 clients to obtain authorization from an OAuth authorization server without requiring the two parties to interact before hand. Nevertheless, in order 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 OAuth2 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 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.
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 display name and icon to be presented to the user during the authorization step. This draft provides a method for the client to register and update this information over time.
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:
[[ Following are proposed requirements for dynamic client registration. This section is intended for discussion and will likely be removed in the final draft. ]]
In order for an authorization server to do proper user-delegated authorization and prevent unauthorized access it must be able to identify clients uniquely. As is done today in OAuth, the client identifier (and optional secret) should thus be issued by the authorization server and not simply accepted as proposed by the client.
In order for the authorization server to describe a client to an end-user in an authorization step it needs information about the client. This can be the client name at a minimum, but today servers usually request at least a description, a homepage URL, and an icon when doing manual registration.
In order to prevent spoofing of clients and enable dynamic building of strong trust relationships, the authorization server should have the option to verify the provided information. This might be solved using message signature verification.
Each instance of a native application (that is, the specific instance running on each device) that is installed and run by the same user may need the option of getting a unique client identifier. In this case, there are implications around gathering and displaying enough information to ensure that the end-user is delegating authorization to the intended application. The registration protocol should be simple and flexible enough to allow for multiple types of applications.
When a client sends information to a server endpoint, it might take time for this data to propagate through big server installations that spread across various data centers. Care needs to be taken that subsequent interactions with the user after the registration process, such as an authorization request, show the correct data.
Clients generally have an array of metadata associated with their unique Client Identifier at the Authorization Server. These can range from human-facing display strings, such as a client name, to items that impact the security of the protocol, such as the list of valid redirect URIs.
Extensions and profiles of this specification MAY expand this list, but MUST at least accept all parameters on this list. The Authorization Server MUST ignore any additional parameters sent by the Client that it does not understand.
Other Authentication methods may be defined by extension. 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 OAuth2. The extension process is described in OAuth2 Section 2.5, and the value of this parameter MUST be the same as the value of the grant_type parameter defined in the extension.
The Client Registration Endpoint is an OAuth 2.0 Endpoint defined in this document that is designed to allow a Client to register itself with the Authorization Server. The Client Registration Endpoint MUST accept HTTP POST messages with request parameters encoded in the entity body using the application/x-www-form-urlencoded 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 Endpoint defines three operations that a client can take on it, switched by the operation parameter:
The Client Registration Endpoint MAY accept an initial authorization credential in the form of an OAuth 2.0 [RFC6749] access token in order to limit registration to only previously authorized parties. The method by which this access token is obtained by the registrant is generally out-of-band and is out of scope of this specification.
In order to support open registration and facilitate wider interoperability, the Client Registration Endpoint SHOULD allow initial client_register requests with no authentication. These requests MAY be rate-limited or otherwise limited to prevent a denial-of-service attack on the Client Registration Endpoint.
In order to facilitate registered clients updating their information, the Client Registration Endpoint issues a Request Access Token for clients to securely identify themselves in future connections. As such, the Endpoint MUST accept requests with OAuth 2.0 Bearer Tokens [RFC6750] for these operations, whether or not the initial client_register call requires authentication of some form.
These two aspects, operation selection and client authentication, are represented by two parameters common to all operations:
Each operation takes a different parameter set, and all operations are described below.
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 the two parameters described above as well as any parameters described in Client Metadata [client-metadata]. The Authorization Server MAY provision default values for any items omitted in the Client Metadata.
Following is a non-normative example request (with line wraps for display purposes only):
POST /register HTTP/1.1
Accept: application/x-www-form-urlencoded
Host: server.example.com
operation=client_register
&redirect_uris=https://client.example.org/callback
%20https://client.example.org/callback2
&client_name=My%20Example%20Client
&token_endpoint_auth_type=client_secret_basic%20client_secret_post
&scope=read%20write%20dolphin
&logo_url=https://client.example.org/logo.png
&jwk_url=https://client.example.org/my_rsa_public_key.jwk
Upon successful registration, the Client Registration Endpoint returns the newly-created Client Identifier and, if applicable, a Client Secret, along with 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 field values and substitute them with suitable values. If this happens, the Authorization Server MUST include these fields in the response to the client.
The response also contains a Registration Access Token that is to be used by the client to perform subsequent operations at this endpoint, such as client_update and rotate_secret.
All of the response items are returned as a JSON document [RFC4627] with the following fields as top-level members of the root JSON object.
Following is a non-normative example response:
HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
{
"client_id":"s6BhdRkqt3",
"client_secret": "cf136dc3c1fc93f31185e5885805d",
"scope": "read write dolphin",
"grant_type": "authorization_code refresh_token",
"token_endpoint_auth_type": "client_secret_basic client_secret_post",
"logo_url": "https://client.example.org/logo.png",
"jwk_url": "https://client.example.org/my_rsa_public_key.jwk",
"registration_access_token": "reg-23410913-abewfq.123483",
"expires_at":2893276800
}
This operation updates a previously-registered client with new metadata at the Authorization Server. This request MUST be protected by the Registration Authorization Token associated with the Client. This request MAY include any fields described in Client Metadata [client-metadata]. If included in the request, valid values of Client Metadata fields in this request MUST replace, not augment, the values previously associated with this Client. Empty values in Client Metadata MUST be taken as a request to clear any existing value of that field. Omitted values in the Client Metadata MUST remain unchanged by the Authorization Server. The Authorization Server MAY replace any invalid values with suitable values.
Following is a non-normative example request (with line wraps for display purposes only):
POST /register HTTP/1.1
Accept: application/x-www-form-urlencoded
Host: server.example.com
Authorization: Bearer reg-23410913-abewfq.123483
operation=client_update
&redirect_uri=https://client.example.org/callback
%20https://client.example.org/alt
&client_name=My%20New%20Example%20
&logo_url=https://client.example.org/newlogo.png
Upon successful update, the Client Registration Endpoint returns the Client ID, along with all current 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 field values and substitute them suitable values. If this happens, the Authorization Server MUST include these fields in the response to the client.
The Authorization Server MUST NOT include the Client Secret or Request Access Token in this response.
These fields are returned in a JSON Document [RFC4627] as top-level members of the root JSON object.
Following is a non-normative example response:
HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
{
"client_id": "s6BhdRkqt3",
"client_name": "My New Example",
"redirect_uri":
"https://client.example.org/callback https://client.example.org/alt"
"scope": "read write dolphin",
"grant_type": "authorization_code refresh_token",
"token_endpoint_auth_type": "client_secret_basic client_secret_post",
"logo_url": "https://client.example.org/newlogo.png",
"jwk_url": "https://client.example.org/my_rsa_public_key.jwk",
}
This operation allows the client to rotate its current Registration Access Token as well as its Client Secret, if it has one.
Following is a non-normative example request (with line wraps for display purposes only):
POST /register HTTP/1.1 Accept: application/x-www-form-urlencoded Host: server.example.com Authorization: Bearer reg-23410913-abewfq.123483 operation=rotate_secret
Upon successful rotation of the Registration Access Token, and optionally the Client Secret, the Client Registration Endpoint returns a JSON document [RFC4627] with the following fields as top-level members of the root JSON object. This response MUST NOT include any other client metadata.
Following is a non-normative example response:
HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
{
"client_id":"s6BhdRkqt3",
"client_secret": "7fce6c93f31185e5885805d",
"registration_access_token": "reg-02348913-oieqer.983421",
"expires_at":2893276800
}
The Authorization Server SHOULD discard and invalidate the Request Access Token and the Client Secret associated with this Client after successful completion of this request.
When an OAuth error condition occurs, the Client Registration Endpoint returns an Error Response as defined in Section 5.2 of the OAuth 2.0 specification.
When a registration error condition occurs, the Client Registration Endpoint returns a HTTP 400 status code including 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
{
"error":"invalid_operation",
"error_description":"The value of the operation parameter must
be one of client_register, rotate_secret or client_update."
}
This document makes no requests of IANA.
[[ Editor's note: Following are some security considerations taken from the UMA and OpenID Connect source drafts. These need to be massaged into a properly generic set of considerations. ]]
Since requests to the Client Registration Endpoint result in the transmission of clear-text credentials (in the HTTP request and response), the 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].
As this endpoint is an OAuth2 Protected Resource, requests to the Registration Endpoint SHOULD have some rate limiting on failures to prevent the Registration Access Token from being disclosed though repeated access attempts.
The authorization server MUST treat all client metadata as self-asserted. A rogue Client might use the name and logo for the legitimate Client, which it is trying to impersonate. An Authorization Server needs to take steps to mitigate this phishing risk, since the logo could confuse users into thinking they're logging in to the legitimate Client. For instance, an Authorization Server could warn if the domain/site of the logo doesn't match the domain/site of redirect URIs. An Authorization Server can also present warning messages to end users about untrusted Clients in all cases, especially if such clients have been dynamically registered and 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_url and policy_url). A rogue Client could specify a registration request with a reference to a drive-by download in the policy_url. The Authorization Server should check to see if the logo_url and policy_url have the same host as the hosts defined in the array of redirect_uris.
While the Client Secret can expire, the Registration Access Token should not expire while a client is still actively registered. If this token were to expire, a Client could be left in a situation where it has no means of updating itself and must register itself anew. As the Registration Access Tokens are long-term credentials, they MUST be protected by the Client as a secret. [[ Editor's note: with the right error codes returned from client_update, the AS could force the Client to call rotate_secret before going forward, lessening the window for abuse of a leaked registration token. ]]
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: Torsten Lodderstedt, Eve Maler, Thomas Hardjono, Christian Scholz, Nat Sakimura, George Fletcher, Amanda Anganes, and Domenico Catalano.
[[ to be removed by RFC editor before publication as an RFC ]]
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