draft-oauth-client-registration.txt

Network Working Group                                     C. Scholz, Ed.
Internet-Draft                                           COM.lounge GmbH
Intended status: Standards Track                             M. Machulak
Expires: February 12, 2011                          Newcastle University
                                                                E. Maler
                                                                  PayPal
                                                         August 11, 2010


               OAuth Dynamic Client Registration Protocol
                     draft-oauth-dyn-reg-v1-00.txt

Abstract

   This specification proposes an OAuth Dynamic Client Registration
   protocol.

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 12, 2011.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.



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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Notational Conventions . . . . . . . . . . . . . . . . . .  3
     1.2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Use Cases  . . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Requirements . . . . . . . . . . . . . . . . . . . . . . . . .  5
     3.1.  The client needs to be uniquely identifiable by the
           authorization server . . . . . . . . . . . . . . . . . . .  5
     3.2.  The authorization server must collect metadata about a
           client for later user interaction  . . . . . . . . . . . .  5
     3.3.  The authorization server must have the option of
           strongly authenticating the client and its metadata  . . .  5
     3.4.  Dynamic client registration must be possible from both
           web-server applications and applications with other
           capabilities and limitations, such as native
           applications . . . . . . . . . . . . . . . . . . . . . . .  6
     3.5.  Transaction integrity must be ensured in large
           deployments where data propagation can be an issue . . . .  6
     3.6.  UMA design principles and requirements . . . . . . . . . .  6
   4.  Analysis of Registration Flow Options  . . . . . . . . . . . .  7
   5.  Discovery of Server's Client Registration Endpoint . . . . . .  8
   6.  Client Registration with Pushed Metadata . . . . . . . . . . .  9
     6.1.  Client Registration Request  . . . . . . . . . . . . . . .  9
     6.2.  Client Registration Response . . . . . . . . . . . . . . . 10
     6.3.  Error Response . . . . . . . . . . . . . . . . . . . . . . 11
   7.  Client Registration with Pushed URL and Pulled Metadata  . . . 12
     7.1.  Client Registration Request  . . . . . . . . . . . . . . . 13
     7.2.  Client Discovery . . . . . . . . . . . . . . . . . . . . . 14
     7.3.  Client Registration Response . . . . . . . . . . . . . . . 15
     7.4.  Error Response . . . . . . . . . . . . . . . . . . . . . . 16
   8.  Native Application Client Registration . . . . . . . . . . . . 17
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 18
   Appendix A.  Acknowledgements  . . . . . . . . . . . . . . . . . . 18
   Appendix B.  Document History  . . . . . . . . . . . . . . . . . . 19
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 19
     10.2. Non-Normative References . . . . . . . . . . . . . . . . . 19
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20












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1.  Introduction

   This informal draft discusses a number of requirements for and
   approaches to automatic registration of clients with an OAuth
   authorization server, with special emphasis on the needs of the
   OAuth-based User-Managed Access protocol [UMA-Core].

   In some use-case scenarios it is desirable or necessary to allow
   OAuth clients to obtain authorization from an OAuth authorization
   server without the two parties having previously interacted.
   Nevertheless, in order for the authorization server to accurately
   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 goal of this proposed registration protocol is for an
   authorization server to provide a client with a client identifier and
   optionally a client secret in a dynamic fashion.  To accomplish this,
   the authorization server must first be provided with information
   about the client, with the client-name being the minimal information
   provided.  In practice, additional information will need to be
   furnished to the authorization server, such as the client's homepage,
   icon, description, and so on.

   The dynamic registration protocol proposed here is envisioned to be
   an additional task to be performed by the OAuth authorization server,
   namely registration of a new client identifier and optional secret
   and the issuance of this information to the client.  This task would
   occur prior to the point at which the client wields its identifier
   and secret at the authorization server in order to obtain an access
   token in normal OAuth fashion.

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

   resource server
         A server capable of accepting and responding to protected
         resource requests.





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   resource owner
         An entity capable of granting access to a protected resource.

   client
         An application obtaining authorization and making protected
         resource requests.

   authorization server
         A server capable of issuing tokens after successfully
         authenticating the resource owner and obtaining authorization.
         The authorization server may be the same server as the resource
         server, or a separate entity.

   authorization manager
         An UMA-defined variant of an authorization server that carries
         out an authorizing user's policies governing access to a
         protected resource.

   end-user authorization endpoint
         The authorization server's HTTP endpoint capable of
         authenticating the end-user and obtaining authorization.

   token endpoint
         The authorization server's HTTP endpoint capable of issuing
         tokens and refreshing expired tokens.

   client identifier
         An unique identifier issued to the client to identify itself to
         the authorization server.  Client identifiers may have a
         matching secret.

   client registration endpoint  The authorization server's HTTP
         endpoint capable of issuing client identifiers and optional
         client secrets.


2.  Use Cases

   The UMA protocol involves two instances of OAuth flows.  In the
   first, an end-user introduces a host (essentially an enhanced OAuth
   resource server) to an authorization manager (an enhanced OAuth
   authorization server) as a client of it, possibly without that host
   having obtained client identification information from that server
   previously.  In the second, a requester (an enhanced OAuth client)
   approaches a host and authorization manager to get and use an access
   token in approximately the normal OAuth fashion, again possibly
   without that client having obtained client identification information
   from that server previously.  Both the host-as-client and the



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   requester-as-client thus may need dynamic client registration in
   order for the UMA protocol flow to proceed.

   The needs for inter-party trust vary in different UMA use cases.  In
   lightweight Web circumstances such as person-to-person calendar
   sharing, dynamic registration is entirely appropriate.  In cases
   where high-sensitivity information is being protected or where a
   regulatory environment puts constraints on the building of trust
   relationships, such as sharing health records with medical
   professionals or giving access to tax records to outsourced
   bookkeeping staff, static means of provisioning client identifiers
   may be imposed.

   More information about UMA use cases is available at [UMA-UC].


3.  Requirements

   Following are proposed requirements for dynamic client registration.

3.1.  The client needs to be uniquely identifiable by the authorization
      server

   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.

3.2.  The authorization server must collect metadata about a client for
      later user interaction

   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.

3.3.  The authorization server must have the option of strongly
      authenticating the client and its metadata

   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; relatively weaker
   authentication might be achieved in a simpler way by pulling metadata
   from a trusted client URL.



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3.4.  Dynamic client registration must be possible from both web-server
      applications and applications with other capabilities and
      limitations, such as native applications

   In the UMA context, alternative types of applications might serve as
   both hosts (for example, as a device-based personal data store) and
   requesters (for example, to subscribe to a calendar or view a photo).
   Such applications, particularly native applications, may have special
   limitations, so new solutions to meeting the set of requirements
   presented here may be needed.  We anticipate that 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.

3.5.  Transaction integrity must be ensured in large deployments where
      data propagation can be an issue

   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.

   In the UMA context, dynamic registration of a host at an AM is almost
   certain to take place in the middle of an introduction and
   authorization process mediated by the end-user; even though the host
   needs a client identifier from the AM no matter which end-user caused
   the registration process to take place, the end-user may need to wait
   for the registration sub-process to finish in order to continue with
   the overall process.  It may be necessary to ensure that the host
   interacts with the same AM server throughout.

3.6.  UMA design principles and requirements

   In addition to general requirements for dynamic client registration,
   UMA seeks to optimize for the design principles and requirements
   found in the UMA Requirements document [UMA-Reqs], most particularly:

   o  DP1: Simple to understand, implement in an interoperable fashion,
      and deploy on an Internet-wide scale

   o  DP6: Able to be combined and extended to support a variety of use
      cases and emerging application functionality





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   o  DP8: Avoid adding crypto requirements beyond what existing web app
      implementations do today

   o  DP10: Complexity should be borne by the authorization endpoint vs.
      other endpoints


4.  Analysis of Registration Flow Options

   This section analyzes some options for exchanging client metadata for
   a client identifier and optional secret.

   It currently seems impossible to specify a single registration flow
   that will satisfy all requirements, deployment needs, and client
   types.  This document, therefore, presents as small a variety of
   options as possible.  If it is possible to construct a single unified
   flow in the ultimate design, all other things being equal this would
   be preferred.

   Client provides metadata on every request
         In this approach, the client passes all necessary metadata such
         as its name and icon on every request to the authorization
         server, and the client doesn't wield a client identifier as
         such.  This option makes it more difficult (though not
         impossible) to meet the first and second requirements since
         different clients could theoretically represent themselves to
         an authorization server with the same metadata and the same
         client could represent itself on subsequent visits with
         different metadata.  Also, today's OAuth protocol requires the
         use of a client identifier.  Because of the UMA simplicity
         principle we do not recommend this flow option and and have not
         provided a candidate solution.

   Client pushes metadata
         In this approach, the client discovers the registration
         endpoint of the authorization server and sends its metadata
         directly to that endpoint in a standard format.  The
         authorization server answers with a client identifier and
         optional secret in the response.  This approach may be
         necessary in cases where the client is behind a firewall, but
         strong authentication of the client metadata may be more
         difficult or costly with this approach than with a "pull"
         approach, discussed just below.  Further, this approach is
         problematic in the case of applications that can't function as
         POST-capable web servers.  A proposal for "push" is presented
         in this document.





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   Client pushes URL, server pulls metadata from it
         In this approach, the client sends only a URL to the
         authorization server, which then uses that URL to pull metadata
         about the client in some standard format, returning
         identification information in the response to the initial
         request.  This approach more easily allows for strong
         authentication of clients because the metadata can be
         statically signed.  (The message containing the URL could be
         signed as well.)  However, caution should be exercised around
         the propagation issue if the initial URL push is made to a
         server different from the one the end-user is interacting with.
         Further, this approach is problematic in the case of
         applications that cannot themselves serve as "pull-able"
         metadata repositories.  A proposal for "pull" is presented in
         this document.

   Native-app client collaborates with home-base web app to provide
   metadata
         An instance of a native application (for example, on a mobile
         device) may have difficulty directly conveying trustworthy
         metadata but may also have difficulty providing a trustworthy
         third-party source from which a server can pull metadata.  This
         document explores one option for meeting the requirements, but
         does not present a full-fledged proposal.


5.  Discovery of Server's Client Registration Endpoint

   Regardless of flow option, the client needs to discover the
   authorization server's client registration endpoint.

   The client MUST use the [RFC5785] and [hostmeta] discovery mechanisms
   to learn the URI of the client registration endpoint at the
   authorization server.  The authorization server MUST provide a host-
   meta document containing a Link element with a rel value of:
   "http://oauth.net/as/registration"

   For example:


         <XRD>
           <Host>http://server.example.com</Host>
           <Link rel="http://oauth.net/as/registration"
                 href="https://server.example.com/register">
               <Title>Client Registration Endpoint</Title>
           </Link>
         </XRD>




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6.  Client Registration with Pushed Metadata

   This registration flow works as follows:

   1.  The client sends its metadata in JSON form to the client
       registration endpoint.  The client MUST send its name,
       description, and redirection URI and MAY send a URI for its icon.
       The client MAY sign the metadata as a JSON Token issuer, using
       the mechanisms defined in [OAuth-Sig].

   2.  The authorization server checks the data, verifying the signature
       as necessary, and returns a client identifier and an optional
       client secret.



     +--------+                                  +---------------+
     | Client |--(A)--- Registration Request --->| Authorization |
     |        |         with Metadata            |     Server    |
     |        |                                  |               |
     |        |<-(B)----Registration Response ---|               |
     |        |         with Client ID Info      |               |
     +--------+                                  +---------------+


          Figure 1: Client Registration Flow with Pushed Metadata

6.1.  Client Registration Request

   The client sends a JSON formatted document to the client registration
   endpoint.  The client includes the following parameters in the
   request:

   type
         REQUIRED.  This parameter must be set to "push".

   client_name
         REQUIRED.  This field contains a human-readable name of the
         client.

   client_url
         REQUIRED.  This field contains the URL of the homepage of the
         client.

   client_description
         REQUIRED.  This field contains a text description of the
         client.




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   client_icon
         OPTIONAL.  This field contains a URL for an icon for the
         client.

   redirect_url
         REQUIRED.  This field contains the URL to which the
         authorization server should send its response.

   The client MAY include additional metadata in the request and the
   authorization server MAY ignore this additional information.

   For example, the client might send the following request:


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

       {
         type: "push",
         client_name: "Online Photo Gallery",
         client_url:  "http://onlinephotogallery.com",
         client_description: "Uploading and also editing capabilities!",
         client_icon: "http://onlinephotogallery.com/icon.png",
         redirect_url: "https://onlinephotogallery.com/client_reg"
       }


   The parameters are included in the entity body of the HTTP request
   using the "application/json" media type as defined by [JSON].  The
   parameters are serialized into a JSON structure by adding each
   parameter at the highest structure level.  Parameter names and string
   values are included as JSON strings.

6.2.  Client Registration Response

   After receiving and verifying information received from the client,
   the authorization server issues a client identifier and an optional
   client secret, and constructs the response by adding the following
   parameters to the entity body of the HTTP response with a 200 status
   code (OK):

   client_id
         REQUIRED.







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   client_secret
         OPTIONAL.

   issued_at
         OPTIONAL.  Specifies the timestamp when the identifier was
         issued.  The timestamp value MUST be a positive integer.  The
         value is expressed in the number of seconds since January 1,
         1970 00:00:00 GMT.

   expires_in
         OPTIONAL; if supplied, the "issued_at" parameter is REQUIRED.
         Specifies the valid lifetime, in seconds, of the identifier.
         The value is represented in base 10 ASCII.

   The parameters are included in the entity body of the HTTP response
   using the "application/json" media type as defined by [JSON].  The
   parameters are serialized into a JSON structure by adding each
   parameter at the highest structure level.  Parameter names and string
   values are included as JSON strings.

   The authorization server MUST include the HTTP "Cache-Control"
   response header field with a value of "no-store" in any response
   containing "client_secret".

   For example, the authorization server might return the following
   response:


       HTTP/1.1 200 OK
       Content-Type: application/json
       Cache-Control: no-store

       {
         client_id: "5UO9XcL4TQTa",
         client_secret: "WdRKN3zeTc20"
       }


6.3.  Error Response

   If the request for registration is invalid or unauthorized, the
   authorization server constructs the response by adding the following
   parameters to the entity body of the HTTP response with a 400 status
   code (Bad Request) using the "application/json" media type:

   o  "error" (REQUIRED).





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   o  "error_description" (OPTIONAL).  Human-readable text providing
      additional information, used to assist in the understanding and
      resolution of the error occurred.

   o  "error_uri" (OPTIONAL).  A URI identifying a human-readable web
      page with information about the error, used to provide the end-
      user with additional information about the error.

   An example error response (with line breaks for readability):


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

       {
       "error": "unauthorized_client",
       "description": "This client is not on the
         white list of this Authorization Server."
       }



7.  Client Registration with Pushed URL and Pulled Metadata

   This registration flow works as follows:

   1.  The client sends its metadata URI to the client registration
       endpoint.  The client MAY sign the metadata as a JSON Token
       issuer, using the mechanisms defined in [OAuth-Sig].

   2.  The authorization server verifies the signature as necessary, and
       uses the [RFC5785] and [hostmeta] discovery mechanisms on this
       URI to retrieve the host-meta document describing the client.
       The host-meta document MUST contain the client name, description,
       and redirection URI, and MAY contain a URI for the client icon.















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     +--------+                                  +---------------+
     | Client |--(A)--- Registration Request --->| Authorization |
     |        |         with URL                 |     Server    |
     |        |                                  |               |
     |        |<-(B)--- Client Discovery --------|               |
     |        |                                  |               |
     |        |--(C)---- Host-Meta Document ---->|               |
     |        |                                  |               |
     |        |<-(D)--- Registration Response ---|               |
     |        |         with Client ID Info      |               |
     +--------+                                  +---------------+


       Figure 2: Client Registration Flow with Pushed URL and Pulled
                                 Metadata

7.1.  Client Registration Request

   The client sends a JSON formatted document to the client registration
   endpoint.  The client includes the following parameters in the
   request:

   type
         REQUIRED.  This parameter must be set to "pull".

   client_url
         REQUIRED.  This field contains the URL of the homepage of the
         client.

   The client MUST NOT include other metadata parameters, such as those
   defined in the pushed-metadata scenario.

   For example, the client might send the following request:


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

       {
         type: "pull",
         url: "http://onlinephotogallery.com"
       }



   The parameters are included in the entity body of the HTTP request
   using the "application/json" media type as defined by [JSON].  The



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   parameters are serialized into a JSON structure by adding each
   parameter at the highest structure level.  Parameter names and string
   values are included as JSON strings.

7.2.  Client Discovery

   The authorization server evaluates this request and MAY perform a
   [RFC5785] and [hostmeta] discovery mechanism on the provided URL to
   the host-meta document for the client.

   For example:


   GET /.well-known/host-meta HTTP/1.1
   Host: onlinephotogallery.com

   The authorization server retrieves the host-meta document, which MUST
   contain:

   o  A "Property" element with a "type" value of
      "http://oauth.net/client/name" containing the human-readable
      client name.  (REQUIRED)

   o  A "Property" element with a "type" value of
      "http://oauth.net/client/description" containing the human
      readable description of the client.  (REQUIRED)

   o  A "Link" element with a "rel" value of
      "http://oauth.net/client/redirect_uri" (REQUIRED).

   o  A "Link" element with a "rel" value of
      "http://oauth.net/client/uri" (REQUIRED).

   o  A "Link" element with a "rel" value of
      "http://oauth.net/client/icon" (OPTIONAL).
















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   For example:


       <XRD>
         <Host>http://onlinephotogallery.com</Host>
         <Property type="http://oauth.net/client/name">
           Online Photo Gallery
         </Property>
         <Property type="http://oauth.net/client/description">
           Really nice Online Photo Gallery!
         </Property>
         <Link rel="http://oauth.net/client/uri"
               href="http://onlinephotogallery.com">
           <Title>Client URI</Title>
         </Link>
         <Link rel="http://oauth.net/client/redirect_uri"
               href="https://onlinephotogallery.com/client_reg">
           <Title>Client Redirect URI</Title>
         </Link>
         <Link rel="http://oauth.net/client/icon"
               href="http://onlinephotogallery.com/icon.png">
           <Title>Client Icon</Title>
         </Link>
       </XRD>


7.3.  Client Registration Response

   After receiving and verifying information retrieved from the client,
   the authorization server issues the client identifier and an optional
   client secret, and constructs the response by adding the following
   parameters to the entity body of the HTTP response with a 200 status
   code (OK):

   o  "client_id" (REQUIRED)

   o  "client_secret" (OPTIONAL)

   The parameters are included in the entity body of the HTTP response
   using the "application/json" media type as defined by [JSON].  The
   parameters are serialized into a JSON structure by adding each
   parameter at the highest structure level.  Parameter names and string
   values are included as JSON strings.

   The authorization server MUST include the HTTP "Cache-Control"
   response header field with a value of "no-store" in any response
   containing the "client_secret".




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   For example the authorization server might return the following
   response:


       HTTP/1.1 200 OK
       Content-Type: application/json
       Cache-Control: no-store

       {
         "client_id":"5UO9XcL4TQTa",
         "client_secret":"WdRKN3zeTc20"
       }


7.4.  Error Response

   If the request for registration is invalid or unauthorized, the
   authorization server constructs the response by adding the following
   parameters to the entity body of the HTTP response with a 400 status
   code (Bad Request) using the "application/json" media type:

   o  "error" (REQUIRED).  A single error code.

   o  "error_description" (OPTIONAL).  Human-readable text providing
      additional information, used to assist in the understanding and
      resolution of the error occurred.

   o  "error_uri" (OPTIONAL).  A URI identifying a human-readable web
      page with information about the error, used to provide the end-
      user with additional information about the error.

   An example error response (with line breaks for readability):


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

       {
       "error": "unauthorized_client",
       "description": "This client is not on the
         white list of this Authorization Server."
       }


   If the host-meta discovery was not successful, the authorization
   server MUST use the error code "hostmeta_error".




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   An example error response (with line breaks for readability):


       HTTP/1.1 404 Not Found
       Content-Type: application/json
       Cache-Control: no-store

       {
       "error": "hostmeta_error",
       "description": "The hostmeta document could
         not be retrieved from the URL."
       }



8.  Native Application Client Registration

   For a native application serving as an UMA host, we anticipate that
   the need for dynamic client registration to introduce this app to an
   UMA authorization manager may typically happen only once (or very
   infrequently), likely to a single authorization manager, and
   registration could usefully take place at the time the app is
   provisioned onto a device.  By contrast, for a native app serving as
   an UMA requester, it may need to register at multiple authorization
   managers over time when seeking access tokens, at moments much later
   than the original provisioning of the app onto the device.

   When a native application is provisioned on a device, such as through
   an app store model, often it has an associated "home base" web server
   application component with which it registers (outside of any UMA-
   related or OAuth-related interactions).  This pairwise relationship
   can be exploited in a number of ways to allow trustable, unique
   metadata to be conveyed to an OAuth server and for this instance of
   the app to receive a client identifier and optional secret.  We have
   discussed "device-initiated" and "home base-initiated" pattern
   options for OAuth dynamic client registration in these circumstances.
   Device-initiated flows seem more generically applicable (for example,
   for both UMA host and UMA requester needs).  However, a home base-
   initiated flow may be preferable in case it is necessary to pre-
   determine a trust level towards an OAuth server.  In this case, the
   home base server could initiate the registration process if and only
   if there exists a trust relationship between the two parties.

   Following is one option for a device-initiated flow:

   1.  User provisions native app on device and registers with and
       authenticates to app's home-base web application.




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   2.  Home base provisions native app with home base-signed metadata.

   3.  Whenever user tries to use native app to access a protected
       resource, native app provides home base-provided metadata to
       server.

   4.  Server verifies home base signature by pulling public key from
       home base URL and generates client identifier and secret for
       native app.

   5.  Server returns client identifier and secret to native app.


9.  Security Considerations

   Following are some security considerations:

   o  No client authentication: The server should treat unsigned pushed
      client metadata as self-asserted.

   o  Weak client authentication: The server should treat unsigned
      pulled client metadata as self-asserted unless the the domain of
      the client matches the client metadata URL and the URL is well-
      known and trusted.

   o  Strong client authentication: The server should treat signed
      client metadata (pushed or pulled) and a signed metadata URL as
      self-asserted unless it can verify the signature as being from a
      trusted source.


Appendix A.  Acknowledgements

   The authors thank the User-Managed Access Work Group participants,
   particularly the following, for their input to this document:

   o  Domenico Catalano

   o  George Fletcher

   o  Thomas Hardjono

   o  Nat Sakimura








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Appendix B.  Document History

   [[ to be removed by RFC editor before publication as an RFC ]]


10.  References

10.1.  Normative References

   [JSON]     Crockford, D., "The application/json Media Type for
              JavaScript Object Notation (JSON)", 2006,
              <http://tools.ietf.org/html/rfc4627>.

   [OAuth-Sig]
              Balfanz, D., "OAuth Signature proposals", 2010, <http://
              www.ietf.org/mail-archive/web/oauth/current/
              msg03893.html>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2617]  Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
              Leach, P., Luotonen, A., and L. Stewart, "HTTP
              Authentication: Basic and Digest Access Authentication",
              RFC 2617, June 1999.

   [RFC5785]  Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known
              Uniform Resource Identifiers (URIs)", RFC 5785,
              April 2010.

   [hostmeta]
              Hammer-Lahav, E., "Web Host Metadata", 2010, <http://
              xml.resource.org/public/rfc/bibxml3/
              reference.I-D.draft-hammer-hostmeta-13.xml>.

10.2.  Non-Normative References

   [UMA-Core]
              Scholz, C., "UMA Requirements", 2010, <http://
              kantarainitiative.org/confluence/display/uma/
              Working+Drafts>.

   [UMA-Reqs]
              Maler, E., "UMA Requirements", 2010, <http://
              kantarainitiative.org/confluence/display/uma/
              UMA+Requirements>.

   [UMA-UC]   Akram, H., "UMA Explained", 2010, <http://



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              kantarainitiative.org/confluence/display/uma/
              UMA+Scenarios+and+Use+Cases>.


Authors' Addresses

   Christian Scholz (editor)
   COM.lounge GmbH

   Email: cs@comlounge.net
   URI:   http://comlounge.net


   Maciej Machulak
   Newcastle University

   Email: m.p.machulak@ncl.ac.uk
   URI:   http://ncl.ac.uk/


   Eve Maler
   PayPal

   Email: eve@xmlgrrl.com
   URI:   http://www.paypal.com/


























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