OAuth Working Group J. Richer, Ed. Internet-Draft Intended status: Standards Track M. Jones Expires: September 24, 2015 Microsoft J. Bradley Ping Identity M. Machulak Newcastle University P. Hunt Oracle Corporation March 23, 2015 OAuth 2.0 Dynamic Client Registration Protocol draft-ietf-oauth-dyn-reg-25 Abstract This specification defines mechanisms for dynamically registering OAuth 2.0 clients with authorization servers. Registration requests send a set of desired client metadata values to the authorization server. The resulting registration responses return a client identifier to use at the authorization server and the client metadata values registered for the client. The client can then use this registration information to communicate with the authorization server using the OAuth 2.0 protocol. This specification also defines a set of common client metadata fields and values for clients to use during registration. Status of This Memo This 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 September 24, 2015. Richer, et al. Expires September 24, 2015 [Page 1] Internet-Draft OAuth 2.0 Dynamic Registration March 2015 Copyright Notice Copyright (c) 2015 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Notational Conventions . . . . . . . . . . . . . . . . . 4 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 1.3. Protocol Flow . . . . . . . . . . . . . . . . . . . . . . 5 2. Client Metadata . . . . . . . . . . . . . . . . . . . . . . . 6 2.1. Relationship between Grant Types and Response Types . . . 10 2.2. Human-Readable Client Metadata . . . . . . . . . . . . . 11 2.3. Software Statement . . . . . . . . . . . . . . . . . . . 12 3. Client Registration Endpoint . . . . . . . . . . . . . . . . 13 3.1. Client Registration Request . . . . . . . . . . . . . . . 14 3.1.1. Client Registration Request Using a Software Statement . . . . . . . . . . . . . . . . . . . . . . 16 3.2. Responses . . . . . . . . . . . . . . . . . . . . . . . . 17 3.2.1. Client Information Response . . . . . . . . . . . . . 17 3.2.2. Client Registration Error Response . . . . . . . . . 19 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21 4.1. OAuth Dynamic Registration Client Metadata Registry . . . 21 4.1.1. Registration Template . . . . . . . . . . . . . . . . 21 4.1.2. Initial Registry Contents . . . . . . . . . . . . . . 22 4.2. OAuth Token Endpoint Authentication Methods Registry . . 24 4.2.1. Registration Template . . . . . . . . . . . . . . . . 25 4.2.2. Initial Registry Contents . . . . . . . . . . . . . . 25 5. Security Considerations . . . . . . . . . . . . . . . . . . . 25 6. Privacy Considerations . . . . . . . . . . . . . . . . . . . 28 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 29 7.1. Normative References . . . . . . . . . . . . . . . . . . 29 7.2. Informative References . . . . . . . . . . . . . . . . . 31 Appendix A. Use Cases . . . . . . . . . . . . . . . . . . . . . 31 A.1. Open versus Protected Dynamic Client Registration . . . . 31 A.1.1. Open Dynamic Client Registration . . . . . . . . . . 31 A.1.2. Protected Dynamic Client Registration . . . . . . . . 31 Richer, et al. Expires September 24, 2015 [Page 2] Internet-Draft OAuth 2.0 Dynamic Registration March 2015 A.2. Registration Without or With Software Statements . . . . 32 A.2.1. Registration Without a Software Statement . . . . . . 32 A.2.2. Registration With a Software Statement . . . . . . . 32 A.3. Registration by the Client or Developer . . . . . . . . . 32 A.3.1. Registration by the Client . . . . . . . . . . . . . 32 A.3.2. Registration by the Developer . . . . . . . . . . . . 32 A.4. Client ID per Client Instance or per Client Software . . 32 A.4.1. Client ID per Client Software Instance . . . . . . . 32 A.4.2. Client ID Shared Among All Instances of Client Software . . . . . . . . . . . . . . . . . . . . . . 33 A.5. Stateful or Stateless Registration . . . . . . . . . . . 33 A.5.1. Stateful Client Registration . . . . . . . . . . . . 33 A.5.2. Stateless Client Registration . . . . . . . . . . . . 33 Appendix B. Acknowledgments . . . . . . . . . . . . . . . . . . 33 Appendix C. Document History . . . . . . . . . . . . . . . . . . 34 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 39 1. Introduction In order for an OAuth 2.0 [RFC6749] client to utilize an OAuth 2.0 authorization server, the client needs specific information to interact with the server, including an OAuth 2.0 client identifier to use at that server. This specification describes how an OAuth 2.0 client can be dynamically registered with an authorization server to obtain this information. As part of the registration process, this specification also defines a mechanism for the client to present the authorization server with a set of metadata, such as a set of valid redirection URIs. This metadata can either be communicated in a self-asserted fashion or as a set of metadata called a software statement, which is digitally signed or 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 specification 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. Richer, et al. Expires September 24, 2015 [Page 3] Internet-Draft OAuth 2.0 Dynamic Registration March 2015 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 Software Software implementing an OAuth 2.0 client. Client Instance A deployed instance of a piece of client software. Client Developer The person or organization that builds a client software package and prepares it for distribution. At the time of building the client, the developer is often not aware of who the deploying service provider organizations will be. Client developers will need to use dynamic registration when they are unable to predict aspects of the software, such as the deployment URLs, at compile time. For instance, this can occur when the software API publisher and the deploying organization are not the same. Client Registration Endpoint OAuth 2.0 endpoint through which a client can be registered at an authorization server. The means by which the URL for this endpoint is obtained are out of scope for this specification. Initial Access Token OAuth 2.0 access token optionally issued by an authorization server to a developer or client and used to authorize calls to the client registration endpoint. The type and format of this token are likely service-specific and are out of scope for this specification. The means by which the authorization server issues this token as well as the means by which the registration endpoint validates this token are out of scope for this specification. Use of an initial access token is required when the authorization server limits the parties that can register a client. Richer, et al. Expires September 24, 2015 [Page 4] Internet-Draft OAuth 2.0 Dynamic Registration March 2015 Deployment Organization An administrative security domain under which a software API (service) is deployed and protected by an OAuth 2.0 framework. In some OAuth scenarios, the deployment organization and the software API publisher are the same. In these cases, the deploying organization will often have a close relationship with client software developers. In many other cases, the definer of the service may be an independent third-party publisher or a standards organization. When working to a published specification for an API, the client software developer is unable to have a prior relationship with the potentially many deployment organizations deploying the software API (service). Software API Deployment A deployed instance of a software API that is protected by OAuth 2.0 (a protected resource) in a particular deployment organization domain. For any particular software API, there may be one or more deployments. A software API deployment typically has an associated OAuth 2.0 authorization server as well as a client registration endpoint. The means by which endpoints are obtained are out of scope for this specification. Software API Publisher The organization that defines a particular web accessible API that may be deployed in one or more deployment environments. A publisher may be any standards body, commercial, public, private, or open source organization that is responsible for publishing and distributing software and API specifications that may be protected via OAuth 2.0. In some cases, a software API publisher and a client developer may be the same organization. At the time of publication of a web accessible API, the software publisher often does not have a prior relationship with the deploying organizations. Software Statement 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 client developer. In other cases, a software statement will be issued by a third party organization for use by the client developer. In both cases, the trust relationship the authorization server has with the issuer of the software statement is intended to be used as an input to the evaluation of whether the registration request is accepted. A software statement can be presented to an authorization server as part of a client registration request. 1.3. Protocol Flow Richer, et al. Expires September 24, 2015 [Page 5] Internet-Draft OAuth 2.0 Dynamic Registration March 2015 +--------(A)- Initial Access Token (OPTIONAL) | | +----(B)- Software Statement (OPTIONAL) | | v v +-----------+ +---------------+ | |--(C)- Client Registration Request -->| Client | | Client or | | Registration | | Developer |<-(D)- Client Information Response ---| Endpoint | | | or Client Error Response +---------------+ +-----------+ Figure 1: Abstract Dynamic Client Registration Flow The abstract OAuth 2.0 client dynamic registration flow illustrated in Figure 1 describes the interaction between the client or developer and the endpoint defined in this specification. This figure does not demonstrate error conditions. This flow includes the following steps: (A) Optionally, the client or developer is issued an initial access token giving access to the client registration endpoint. The method by which the initial access token is issued to the client or developer is out of scope for this specification. (B) Optionally, the client or developer is issued a software statement for use with the client registration endpoint. The method by which the software statement is issued to the client or developer is out of scope for this specification. (C) The client or developer calls the client registration endpoint with the client's desired registration metadata, optionally including the initial access token from (A) if one is required by the authorization server. (D) The authorization server registers the client and returns: * the client's registered metadata, * a client identifier that is unique at the server, and * a set of client credentials such as a client secret, if applicable for this client. Examples of different configurations and usages are included in Appendix A. 2. Client Metadata Registered clients have a set of metadata values associated with their client identifier at an authorization server, such as the list of valid redirection URIs or a display name. Richer, et al. Expires September 24, 2015 [Page 6] Internet-Draft OAuth 2.0 Dynamic Registration March 2015 These client metadata values are used in two ways: o as input values to registration requests, and o as output values in registration responses. The following client metadata fields are defined by this specification. The implementation and use of all client metadata fields is OPTIONAL, unless stated otherwise. 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: * "none": The client is a public client as defined in OAuth 2.0 and does not have a client secret. * "client_secret_post": The client uses the HTTP POST parameters defined in OAuth 2.0 section 2.3.1. * "client_secret_basic": the client uses HTTP Basic defined in OAuth 2.0 section 2.3.1 Additional values can be defined via the IANA OAuth Token Endpoint Authentication Methods Registry established in Section 4.2. Absolute URIs can also be used as values for this parameter without being registered. If unspecified or omitted, the default is "client_secret_basic", denoting 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_code": The Authorization Code Grant described in OAuth 2.0 Section 4.1 * "implicit": The Implicit Grant described in OAuth 2.0 Section 4.2 * "password": The Resource Owner Password Credentials Grant described in OAuth 2.0 Section 4.3 * "client_credentials": The Client Credentials Grant described in OAuth 2.0 Section 4.4 * "refresh_token": The Refresh Token Grant described in OAuth 2.0 Section 6. Richer, et al. Expires September 24, 2015 [Page 7] Internet-Draft OAuth 2.0 Dynamic Registration March 2015 * "urn:ietf:params:oauth:grant-type:jwt-bearer": The JWT Bearer Grant defined in OAuth JWT Bearer Token Profiles [OAuth.JWT]. * "urn:ietf:params:oauth:grant-type:saml2-bearer": The SAML 2 Bearer Grant defined in OAuth SAML 2 Bearer Token Profiles [OAuth.SAML2]. If the token endpoint is used in the grant type, the value of this parameter MUST be the same as the value of the "grant_type" parameter passed to the token endpoint defined in the grant type definition. Authorization servers MAY allow for other values as defined in the grant type extension process described in OAuth 2.0 Section 2.5. If omitted, the default behavior is that the client will use only the "authorization_code" Grant Type. response_types Array of the OAuth 2.0 response types that the client can use. These response types are defined as follows: * "code": The authorization code response described in OAuth 2.0 Section 4.1. * "token": The implicit response described in OAuth 2.0 Section 4.2. If the authorization endpoint is used by the grant type, the value of this parameter MUST be the same as the value of the "response_type" parameter passed to the authorization endpoint defined in the grant type definition. Authorization servers MAY allow for other values as defined in the grant type extension process is described in OAuth 2.0 Section 2.5. 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 end-user during authorization. If omitted, the authorization server MAY display the raw "client_id" value to the end-user instead. It is RECOMMENDED that clients always send this field. The value of this field MAY be internationalized, as described in Section 2.2. client_uri URL 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. Richer, et al. Expires September 24, 2015 [Page 8] Internet-Draft OAuth 2.0 Dynamic Registration March 2015 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 contact addresses available to end-users for support requests for the client. See Section 6 for information on Privacy Considerations. 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 both be present in the same request or response. 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 both be present in the same request or response. software_id Richer, et al. Expires September 24, 2015 [Page 9] Internet-Draft OAuth 2.0 Dynamic Registration March 2015 A unique identifier (e.g. a UUID) assigned by the client developer or software publisher used by registration endpoints to identify the client software to be dynamically registered. Unlike "client_id", which is issued by the authorization server and SHOULD vary between instances, the "software_id" SHOULD remain the same for all instances of the client software. The "software_id" SHOULD remain the same across multiple updates or versions of the same piece of software. The value of this field is not intended to be human-readable and is usually opaque to the client and authorization server. software_version A version identifier for the client software identified by "software_id". The value of the "software_version" SHOULD change on any update to the client software identified by the same "software_id". The value of this field is a string that is intended to be compared using string equality matching. The value of this field is not intended to be human readable and is usually opaque to the client and authorization server. Extensions and profiles of this specification MAY expand this list with metadata names and descriptions registered in accordance with the IANA Considerations in Section 4 of this document. The authorization server MUST ignore any client metadata sent by the client that it does not understand (for instance, by silently removing unknown metadata from the client's registration record during processing). 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 Richer, et al. Expires September 24, 2015 [Page 10] Internet-Draft OAuth 2.0 Dynamic Registration March 2015 "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". Richer, et al. Expires September 24, 2015 [Page 11] Internet-Draft OAuth 2.0 Dynamic Registration March 2015 For example, a client could represent its name in English as ""client_name#en": "My Client"" and its name in Japanese as ""client_name#ja-Jpan-JP": "\u30AF\u30E9\u30A4\u30A2\u30F3\u30C8\u540D"" within the same registration request. The authorization server MAY display any or all of these names to the resource owner during the authorization step, choosing which name to display based on system configuration, user preferences or other factors. If any human-readable field is sent without a language tag, parties using it MUST NOT make any assumptions about the language, character set, or script of the string value, and the string value MUST be used as-is wherever it is presented in a user interface. To facilitate interoperability, it is RECOMMENDED that clients and servers use a human-readable field without any language tags in addition to any language-specific fields, and it is RECOMMENDED that any human- readable fields sent without language tags contain values suitable for display on a wide variety of systems. Implementer's Note: Many JSON libraries make it possible to reference members of a JSON object as members of an object construct in the native programming environment of the library. However, while the "#" character is a valid character inside of a JSON object's member names, it is not a valid character for use in an object member name in many programming environments. Therefore, implementations will need to use alternative access forms for these claims. For instance, in JavaScript, if one parses the JSON as follows, "var j = JSON.parse(json);", then as a workaround the member "client_name#en- us" can be accessed using the JavaScript syntax "j["client_name#en- us"]". 2.3. Software Statement A software statement is a JSON Web Token (JWT) [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. It is RECOMMENDED that software statements contain the "software_id" claim to allow authorization servers to correlate different instances of software using the same software statement. For example, a software statement could contain the following claims: Richer, et al. Expires September 24, 2015 [Page 12] Internet-Draft OAuth 2.0 Dynamic Registration March 2015 { "software_id": "4NRB1-0XZABZI9E6-5SM3R", "client_name": "Example Statement-based Client", "client_uri": "https://client.example.net/" } The following non-normative example JWT includes these claims and has been asymmetrically signed using RS256: Line breaks are for display purposes only eyJhbGciOiJSUzI1NiJ9. eyJzb2Z0d2FyZV9pZCI6IjROUkIxLTBYWkFCWkk5RTYtNVNNM1IiLCJjbGll bnRfbmFtZSI6IkV4YW1wbGUgU3RhdGVtZW50LWJhc2VkIENsaWVudCIsImNs aWVudF91cmkiOiJodHRwczovL2NsaWVudC5leGFtcGxlLm5ldC8ifQ. GHfL4QNIrQwL18BSRdE595T9jbzqa06R9BT8w409x9oIcKaZo_mt15riEXHa zdISUvDIZhtiyNrSHQ8K4TvqWxH6uJgcmoodZdPwmWRIEYbQDLqPNxREtYn0 5X3AR7ia4FRjQ2ojZjk5fJqJdQ-JcfxyhK-P8BAWBd6I2LLA77IG32xtbhxY fHX7VhuU5ProJO8uvu3Ayv4XRhLZJY4yKfmyjiiKiPNe-Ia4SMy_d_QSWxsk U5XIQl5Sa2YRPMbDRXttm2TfnZM1xx70DoYi8g6czz-CPGRi4SW_S2RKHIJf IjoI3zTJ0Y2oe0_EJAiXbL6OyF9S5tKxDXV8JIndSA The means by which a client or developer obtains a software statement are outside the scope of this specification. Some common methods could include a client developer generating a client-specific JWT by registering with a software API publisher to obtain a software statement for a class of clients. The 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 Richer, et al. Expires September 24, 2015 [Page 13] Internet-Draft OAuth 2.0 Dynamic Registration March 2015 registration endpoint MUST be protected by a transport-layer security mechanism, as described in Section 5. The client registration endpoint MAY be an OAuth 2.0 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. For example, if the server supports open registration (with no initial access token), the client could send the following registration request to the client registration endpoint: Richer, et al. Expires September 24, 2015 [Page 14] Internet-Draft OAuth 2.0 Dynamic Registration March 2015 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. Richer, et al. Expires September 24, 2015 [Page 15] Internet-Draft OAuth 2.0 Dynamic Registration March 2015 The following is a non-normative example request using an initial access token and registering a JWK set by value (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":[{ "e": "AQAB", "n": "nj3YJwsLUFl9BmpAbkOswCNVx17Eh9wMO-_AReZwBqfaWFcfG HrZXsIV2VMCNVNU8Tpb4obUaSXcRcQ-VMsfQPJm9IzgtRdAY8NN8Xb7PEcYyk lBjvTtuPbpzIaqyiUepzUXNDFuAOOkrIol3WmflPUUgMKULBN0EUd1fpOD70p RM0rlp_gg_WNUKoW1V-3keYUJoXH9NztEDm_D2MQXj9eGOJJ8yPgGL8PAZMLe 2R7jb9TxOCPDED7tY_TU4nFPlxptw59A42mldEmViXsKQt60s1SLboazxFKve qXC_jpLUt22OC6GUG63p-REw-ZOr3r845z50wMuzifQrMI9bQ", "kty": "RSA" }]}, "example_extension_parameter": "example_value" } 3.1.1. Client Registration Request Using a Software Statement In addition to JSON elements, client metadata values MAY also be provided in a software statement, as described in Section 2.3. The authorization server MAY ignore the software statement if it does not support this feature. If the server supports software statements, client metadata values conveyed in the software statement MUST take precedence over those conveyed using plain JSON elements. Software statements are included in the requesting JSON object using this OPTIONAL member: software_statement A software statement containing client metadata values about the client software as claims. Richer, et al. Expires September 24, 2015 [Page 16] Internet-Draft OAuth 2.0 Dynamic Registration March 2015 In the following example, some registration parameters are conveyed as claims in a software statement from the example in Section 2.3, while some values specific to the client instance are conveyed as regular parameters (with line 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":"eyJhbGciOiJSUzI1NiJ9. eyJzb2Z0d2FyZV9pZCI6IjROUkIxLTBYWkFCWkk5RTYtNVNNM1IiLCJjbGll bnRfbmFtZSI6IkV4YW1wbGUgU3RhdGVtZW50LWJhc2VkIENsaWVudCIsImNs aWVudF91cmkiOiJodHRwczovL2NsaWVudC5leGFtcGxlLm5ldC8ifQ. GHfL4QNIrQwL18BSRdE595T9jbzqa06R9BT8w409x9oIcKaZo_mt15riEXHa zdISUvDIZhtiyNrSHQ8K4TvqWxH6uJgcmoodZdPwmWRIEYbQDLqPNxREtYn0 5X3AR7ia4FRjQ2ojZjk5fJqJdQ-JcfxyhK-P8BAWBd6I2LLA77IG32xtbhxY fHX7VhuU5ProJO8uvu3Ayv4XRhLZJY4yKfmyjiiKiPNe-Ia4SMy_d_QSWxsk U5XIQl5Sa2YRPMbDRXttm2TfnZM1xx70DoYi8g6czz-CPGRi4SW_S2RKHIJf IjoI3zTJ0Y2oe0_EJAiXbL6OyF9S5tKxDXV8JIndSA", "scope":"read write", "example_extension_parameter":"example_value" } 3.2. Responses Upon a successful registration request, the authorization server returns a client identifier for the client. The server responds with an HTTP 201 Created code and a body of type "application/json" with content as described in Section 3.2.1. Upon an unsuccessful registration request, the authorization server responds with an error, as described in Section 3.2.2. 3.2.1. Client Information Response The response contains the client identifier as well as the client secret, if the client is a confidential client. The response MAY contain additional fields as specified by extensions to this specification. client_id Richer, et al. Expires September 24, 2015 [Page 17] Internet-Draft OAuth 2.0 Dynamic Registration March 2015 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" and SHOULD be unique for multiple instances of a client using the same "client_id". This value is used by confidential clients to authenticate to the token endpoint as described in OAuth 2.0 [RFC6749] Section 2.3.1. client_id_issued_at OPTIONAL. Time at which the client identifier was issued. The time is represented as the number of seconds from 1970-01-01T0:0:0Z as measured in UTC until the date/time of issuance. client_secret_expires_at REQUIRED if "client_secret" is issued. Time at which the client secret will expire or 0 if it will not expire. The time is represented as the number of seconds from 1970-01-01T0:0:0Z as measured in UTC until the date/time of expiration. Additionally, the authorization server MUST return all registered metadata about this client, including any fields provisioned by the authorization server itself. The authorization server MAY reject or replace any of the client's requested metadata values submitted during the registration and substitute them with suitable values. The 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 unmodified in the response along with other metadata using the "software_statement" member name. Client metadata elements used from the software statement MUST also be returned directly as top-level client metadata values in the registration response (possibly with different values, since the values requested and the values used may differ). Richer, et al. Expires September 24, 2015 [Page 18] Internet-Draft OAuth 2.0 Dynamic Registration March 2015 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" } 3.2.2. Client Registration Error Response When an OAuth 2.0 error condition occurs, such as the client presenting an invalid initial access token, the authorization server returns an error response appropriate to the OAuth 2.0 token type. 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: Richer, et al. Expires September 24, 2015 [Page 19] Internet-Draft OAuth 2.0 Dynamic Registration March 2015 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." } Richer, et al. Expires September 24, 2015 [Page 20] Internet-Draft OAuth 2.0 Dynamic Registration March 2015 4. IANA Considerations 4.1. OAuth Dynamic Registration Client Metadata Registry This specification establishes the OAuth Dynamic Registration Client Metadata registry. OAuth registration client metadata names and descriptions are registered with a Specification Required ([RFC5226]) after a two-week review period on the oauth-ext-review@ietf.org mailing list, on the advice of one or more Designated Experts. However, to allow for the allocation of names prior to publication, the Designated 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. 4.1.1. Registration Template Client Metadata Name: The name requested (e.g., "example"). This name is case sensitive. Names that match other registered names in a case insensitive manner SHOULD NOT be accepted. Client Metadata Description: Brief description of the metadata value (e.g., "Example description"). Change controller: For Standards Track RFCs, 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): Richer, et al. Expires September 24, 2015 [Page 21] Internet-Draft OAuth 2.0 Dynamic Registration March 2015 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. 4.1.2. Initial Registry Contents The initial contents of the OAuth Dynamic Registration Client Metadata registry are: o Client Metadata Name: "redirect_uris" o Client Metadata Description: Array of redirection URIs for use in redirect-based flows o Change controller: IESG o Specification document(s): [[ this document ]] o Client Metadata Name: "token_endpoint_auth_method" o Client Metadata Description: Requested authentication method for the token endpoint o Change controller: IESG o Specification document(s): [[ this document ]] o Client Metadata Name: "grant_types" o Client Metadata Description: Array of OAuth 2.0 grant types that the client may use o Change controller: IESG o Specification document(s): [[ this document ]] o Client Metadata Name: "response_types" o Client Metadata Description: Array of the OAuth 2.0 response types that the client may use o Change controller: IESG o Specification document(s): [[ this document ]] o Client Metadata Name: "client_name" o Client Metadata Description: Human-readable name of the client to be presented to the user o Change Controller: IESG o Specification Document(s): [[ this document ]] o Client Metadata Name: "client_uri" o Client Metadata Description: URL of a Web page providing information about the client o Change Controller: IESG o Specification Document(s): [[ this document ]] o Client Metadata Name: "logo_uri" Richer, et al. Expires September 24, 2015 [Page 22] Internet-Draft OAuth 2.0 Dynamic Registration March 2015 o Client Metadata Description: URL that references a logo for the client o Change Controller: IESG o Specification Document(s): [[ this document ]] o Client Metadata Name: "scope" o Client Metadata Description: Space separated list of OAuth 2.0 scope values o Change Controller: IESG o Specification Document(s): [[ this document ]] o Client Metadata Name: "contacts" o Client Metadata Description: Array of strings representing ways to contact people responsible for this client, typically email addresses o Change Controller: IESG o Specification document(s): [[ this document ]] o Client Metadata Name: "tos_uri" o Client Metadata Description: URL that points to a human-readable Terms of Service document for the client o Change Controller: IESG o Specification Document(s): [[ this document ]] o Client Metadata Name: "policy_uri" o Client Metadata Description: URL that points to a human-readable Policy document for the client o Change Controller: IESG o Specification Document(s): [[ this document ]] o Client Metadata Name: "jwks_uri" o Client Metadata Description: URL referencing the client's JSON Web Key Set [JWK] document representing the client's public keys o Change Controller: IESG o Specification Document(s): [[ this document ]] o Client Metadata Name: "jwks" o Client Metadata Description: Client's JSON Web Key Set [JWK] document representing the client's public keys o Change Controller: IESG o Specification Document(s): [[ this document ]] o Client Metadata Name: "software_id" o Client Metadata Description: Identifier for the software that comprises a client o Change Controller: IESG o Specification Document(s): [[ this document ]] Richer, et al. Expires September 24, 2015 [Page 23] Internet-Draft OAuth 2.0 Dynamic Registration March 2015 o Client Metadata Name: "software_version" o Client Metadata Description: Version identifier for the software that comprises a client o Change Controller: IESG o Specification Document(s): [[ this document ]] o Client Metadata Name: "client_id" o Client Metadata Description: Client identifier o Change Controller: IESG o Specification Document(s): [[ this document ]] o Client Metadata Name: "client_secret" o Client Metadata Description: Client secret o Change Controller: IESG o Specification Document(s): [[ this document ]] o Client Metadata Name: "client_id_issued_at" o Client Metadata Description: Time at which the client identifier was issued o Change Controller: IESG o Specification Document(s): [[ this document ]] o Client Metadata Name: "client_secret_expires_at" o Client Metadata Description: Time at which the client secret will expire o Change Controller: IESG o Specification Document(s): [[ this document ]] 4.2. OAuth Token Endpoint Authentication Methods Registry This specification establishes the OAuth Token Endpoint Authentication Methods registry. Additional values for use as "token_endpoint_auth_method" values are registered with a Specification Required ([RFC5226]) after a two-week review period on the oauth-ext-review@ietf.org mailing list, on the advice of one or more Designated Experts. However, to allow for the allocation of values prior to publication, the Designated 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 Richer, et al. Expires September 24, 2015 [Page 24] Internet-Draft OAuth 2.0 Dynamic Registration March 2015 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. 4.2.1. 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. 4.2.2. Initial Registry Contents The initial contents of the OAuth Token Endpoint Authentication Methods registry are: o Token Endpoint Authorization Method Name: "none" o Change controller: IESG o Specification document(s): [[ this document ]] o Token Endpoint Authorization Method Name: "client_secret_post" o Change controller: IESG o Specification document(s): [[ this document ]] o Token Endpoint Authorization Method Name: "client_secret_basic" o Change controller: IESG o Specification document(s): [[ this document ]] 5. Security Considerations Since requests to the client registration endpoint result in the transmission of clear-text credentials (in the HTTP request and response), the authorization server MUST require the use of a Richer, et al. Expires September 24, 2015 [Page 25] Internet-Draft OAuth 2.0 Dynamic Registration March 2015 transport-layer security mechanism when sending requests to the registration endpoint. The server MUST support TLS 1.2 RFC 5246 [RFC5246] 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]. Implementation security considerations can be found in Recommendations for Secure Use of TLS and DTLS [I-D.ietf-uta-tls-bcp]. For clients that use redirect-based grant types such as "authorization_code" and "implicit", authorization servers MUST require clients to register their redirection URI values. This can help mitigate attacks where rogue actors inject and impersonate a validly registered client and intercept its authorization code or tokens through an invalid redirection URI or open redirector. Additionally, in order to prevent hijacking of the return values of the redirection, registered redirection URI values MUST be one of: o A remote web site protected by TLS (e.g., https://client.example.com/oauth_redirect) o A web site hosted on the local machine using an HTTP URI (e.g., http://localhost:8080/oauth_redirect) o A non-HTTP application-specific URL that is available only to the client application (e.g., exampleapp://oauth_redirect) Public clients MAY register with an authorization server using this protocol, if the authorization server's policy allows them. Public clients use a "none" value for the "token_endpoint_auth_method" metadata field and are generally used with the "implicit" grant type. Often these clients will be short-lived in-browser applications requesting access to a user's resources and access is tied to a user's active session at the authorization server. Since such clients often do not have long-term storage, it is possible that such clients would need to re-register every time the browser application is loaded. 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 Richer, et al. Expires September 24, 2015 [Page 26] Internet-Draft OAuth 2.0 Dynamic Registration March 2015 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 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 Richer, et al. Expires September 24, 2015 [Page 27] Internet-Draft OAuth 2.0 Dynamic Registration March 2015 statement is valid and signed by an acceptable authority (such as the software API publisher), the values of client metadata within the software statement MUST take precedence over those metadata values presented in the plain JSON object, which could have been 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 needs to be very particular about the circumstances under which this occurs. For instance, the authorization server can limit a given client identifier to clients using the same redirect-based flow and the same redirection URIs. An authorization server SHOULD NOT issue the same client secret to multiple instances of a registered client, even if they are issued the same client identifier, or else the client secret could be leaked, allowing malicious impostors to impersonate a confidential client. 6. Privacy Considerations As the protocol described in this specification deals almost exclusively with information about software and not about people, there are very few privacy concerns for its use. The notable exception is the "contacts" field as defined in Client Metadata (Section 2), which contains contact information for the developers or other parties responsible for the client software. These values are intended to be displayed to end-users and will be available to the administrators of the authorization server. As such, the developer may wish to provide an email address or other contact information Richer, et al. Expires September 24, 2015 [Page 28] Internet-Draft OAuth 2.0 Dynamic Registration March 2015 expressly dedicated to the purpose of supporting the client instead of using their personal or professional addresses. Alternatively, the developer may wish to provide a collective email address for the client to allow for continuing contact and support of the client software after the developer moves on and someone else takes over that responsibility. In general, the metadata for a client, such as the client name and software identifier, are common across all instances of a piece of client software and therefore pose no privacy issues for end-users. Client identifiers, on the other hand, are often unique to a specific instance of a client. For clients such as web sites that are used by many users, there may not be significant privacy concerns regarding the client identifier, but for clients such as native applications that are installed on a single end-user's device, the client identifier could be uniquely tracked during OAuth 2.0 transactions and its use tied to that single end-user. However, as the client software still needs to be authorized by a resource owner through an OAuth 2.0 authorization grant, this type of tracking can occur whether or not the client identifier is unique by correlating the authenticated resource owner with the requesting client identifier. Note that clients are forbidden by this specification from creating their own client identifier. If the client were able to do so, an individual client instance could be tracked across multiple colluding authorization servers, leading to privacy and security issues. Additionally, client identifiers are generally issued uniquely per registration request, even for the same instance of software. In this way, an application could marginally improve privacy by registering multiple times and appearing to be completely separate applications. However, this technique does incur significant usability cost in the form of requiring multiple authorizations per resource owner and is therefore unlikely to be used in practice. 7. References 7.1. Normative References [IANA.Language] Internet Assigned Numbers Authority (IANA), "Language Subtag Registry", 2005. [JWK] Jones, M., "JSON Web Key (JWK)", draft-ietf-jose-json-web- key (work in progress), January 2015. [JWS] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Signature (JWS)", draft-ietf-jose-json-web-signature (work in progress), January 2015. Richer, et al. Expires September 24, 2015 [Page 29] Internet-Draft OAuth 2.0 Dynamic Registration March 2015 [JWT] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token (JWT)", draft-ietf-oauth-json-web-token (work in progress), January 2015. [OAuth.JWT] Jones, M., Campbell, B., and C. Mortimore, "JSON Web Token (JWT) Profile for OAuth 2.0 Client Authentication and Authorization Grants", draft-ietf-oauth-jwt-bearer (work in progress), November 2015. [OAuth.SAML2] Campbell, B., Mortimore, C., and M. Jones, "SAML 2.0 Profile for OAuth 2.0 Client Authentication and Authorization Grants", draft-ietf-oauth-saml2-bearer (work in progress), November 2015. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [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. Richer, et al. Expires September 24, 2015 [Page 30] Internet-Draft OAuth 2.0 Dynamic Registration March 2015 7.2. Informative References [I-D.hardjono-oauth-umacore] Hardjono, T., "User-Managed Access (UMA) Profile of OAuth 2.0", draft-hardjono-oauth-umacore-10 (work in progress), July 2014. [I-D.ietf-uta-tls-bcp] Sheffer, Y., Holz, R., and P. Saint-Andre, "Recommendations for Secure Use of TLS and DTLS", draft- ietf-uta-tls-bcp-09 (work in progress), February 2015. [OAuth.Registration.Management] Richer, J., Jones, M., Bradley, J., and M. Machulak, "OAuth 2.0 Dynamic Client Registration Management Protocol", draft-ietf-oauth-dyn-reg-management (work in progress), February 2015. [OpenID.Registration] Sakimura, N., Bradley, J., and M. Jones, "OpenID Connect Dynamic Client Registration 1.0", November 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. Richer, et al. Expires September 24, 2015 [Page 31] Internet-Draft OAuth 2.0 Dynamic Registration March 2015 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 Richer, et al. Expires September 24, 2015 [Page 32] Internet-Draft OAuth 2.0 Dynamic Registration March 2015 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, Richer, et al. Expires September 24, 2015 [Page 33] Internet-Draft OAuth 2.0 Dynamic Registration March 2015 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 [[ to be removed by the RFC editor before publication as an RFC ]] -25 o Updated author information. o Clarified registry contents. o Added forward pointer to IANA from metadata section. o Clarified how to silently ignore errors. o Reformatted diagram text. -24 o Clarified some party definitions. o Clarified the opaqueness of software_id and software_statement. o Created a forward pointer to the Security Considerations section for TLS requirements on the registration endpoint. o Added a forward pointer to the Privacy Considerations section for the contacts field. o Wrote privacy considerations about client_id tracking. -23 o Updated author information. -22 o Reorganized registration response sections. o Addressed shepherd comments. o Added concrete JWK set to example. -21 o Applied minor editorial fixes. o Added software statement examples. o Moved software statement request details to sub-section. o Clarified that a server MAY ignore the software statement (just as it MAY ignore other metadata values). o Removed TLS 1.0. o Added privacy considerations around "contacts" field. o Marked software_id as RECOMMENDED inside of a software statement. -20 Richer, et al. Expires September 24, 2015 [Page 34] Internet-Draft OAuth 2.0 Dynamic Registration March 2015 o Applied minor editorial fixes from working group comments. -19 o Added informative references to the OpenID Connect Dynamic Client Registration and UMA specifications in the introduction. o Clarified the "jwks" and "jwks_uri" descriptions and included an example situation in which they might be used. o Removed "application_type". o Added redirection URI usage restrictions to the Security Considerations section, based on the client type. o Expanded the "tos_uri" and "policy_uri" descriptions. -18 o Corrected an example HTTP response status code to be 201 Created. o Said more about who issues and uses initial access tokens and software statements. o Stated that the use of an initial access token is required when the authorization server limits the parties that can register a client. o Stated that the implementation and use of all client metadata fields is OPTIONAL, other than "redirect_uris", which MUST be used for redirect-based flows and implemented to fulfill the requirement in Section 2 of OAuth 2.0. o Added the "application_type" metadata value, which had somehow been omitted. o Added missing default metadata values, which had somehow been omitted. o Clarified that the "software_id" is ultimately asserted by the client developer. o Clarified that the "error" member is required in error responses, "error_description" member is optional, and other members may be present. o Added security consideration about registrations with duplicate "software_id" and "software_version" values. -17 o Merged draft-ietf-oauth-dyn-reg-metadata back into this document. o Removed "Core" from the document title. o Explicitly state that all metadata members are optional. o Clarified language around software statements for use in registration context. o Clarified that software statements need to be digitally signed or MACed. o Added a "jwks" metadata parameter to parallel the "jwks_uri" parameter. Richer, et al. Expires September 24, 2015 [Page 35] Internet-Draft OAuth 2.0 Dynamic Registration March 2015 o Removed normative language from terminology. o Expanded abstract and introduction. o Addressed review comments from several working group members. -16 o Replaced references to draft-jones-oauth-dyn-reg-metadata and draft-jones-oauth-dyn-reg-management with draft-ietf-oauth-dyn- reg-metadata and draft-ietf-oauth-dyn-reg-management. o Addressed review comments by Phil Hunt and Tony Nadalin. -15 o Partitioned the Dynamic Client Registration specification into core, metadata, and management specifications. This built on work first published as draft-richer-oauth-dyn-reg-core-00 and draft- richer-oauth-dyn-reg-management-00. o Added the ability to use Software Statements. This built on work first published as draft-hunt-oauth-software-statement-00 and draft-hunt-oauth-client-association-00. o Created the IANA OAuth Registration Client Metadata registry for registering Client Metadata values. o Defined Client Instance term and stated that multiple instances can use the same client identifier value under certain circumstances. o Rewrote the introduction. o Rewrote the Use Cases appendix. -14 o Added software_id and software_version metadata fields o Added direct references to RFC6750 errors in read/update/delete methods -13 o Fixed broken example text in registration request and in delete request o Added security discussion of separating clients of different grant types o Fixed error reference to point to RFC6750 instead of RFC6749 o Clarified that servers must respond to all requests to configuration endpoint, even if it's just an error code o Lowercased all Terms to conform to style used in RFC6750 -12 o Improved definition of Initial Access Token Richer, et al. Expires September 24, 2015 [Page 36] Internet-Draft OAuth 2.0 Dynamic Registration March 2015 o Changed developer registration scenario to have the Initial Access Token gotten through a normal OAuth 2.0 flow o Moved non-normative client lifecycle examples to appendix o Marked differentiating between auth servers as out of scope o Added protocol flow diagram o Added credential rotation discussion o Called out Client Registration Endpoint as an OAuth 2.0 Protected Resource o Cleaned up several pieces of text -11 o Added localized text to registration request and response examples. o Removed "client_secret_jwt" and "private_key_jwt". o Clarified "tos_uri" and "policy_uri" definitions. o Added the OAuth Token Endpoint Authentication Methods registry for registering "token_endpoint_auth_method" metadata values. o Removed uses of non-ASCII characters, per RFC formatting rules. o Changed "expires_at" to "client_secret_expires_at" and "issued_at" to "client_id_issued_at" for greater clarity. o Added explanatory text for different credentials (Initial Access Token, Registration Access Token, Client Credentials) and what they're used for. o Added Client Lifecycle discussion and examples. o Defined Initial Access Token in Terminology section. -10 o Added language to point out that scope values are service-specific o Clarified normative language around client metadata o Added extensibility to token_endpoint_auth_method using absolute URIs o Added security consideration about registering redirect URIs o Changed erroneous 403 responses to 401's with notes about token handling o Added example for initial registration credential -09 o Added method of internationalization for Client Metadata values o Fixed SAML reference -08 o Collapsed jwk_uri, jwk_encryption_uri, x509_uri, and x509_encryption_uri into a single jwks_uri parameter o Renamed grant_type to grant_types since it's a plural value Richer, et al. Expires September 24, 2015 [Page 37] Internet-Draft OAuth 2.0 Dynamic Registration March 2015 o Formalized name of "OAuth 2.0" throughout document o Added JWT Bearer Assertion and SAML 2 Bearer Assertion to example grant types o Added response_types parameter and explanatory text on its use with and relationship to grant_types -07 o Changed registration_access_url to registration_client_uri o Fixed missing text in 5.1 o Added Pragma: no-cache to examples o Changed "no such client" error to 403 o Renamed Client Registration Access Endpoint to Client Configuration Endpoint o Changed all the parameter names containing "_url" to instead use "_uri" o Updated example text for forming Client Configuration Endpoint URL -06 o Removed secret_rotation as a client-initiated action, including removing client secret rotation endpoint and parameters. o Changed _links structure to single value registration_access_url. o Collapsed create/update/read responses into client info response. o Changed return code of create action to 201. o Added section to describe suggested generation and composition of Client Registration Access URL. o Added clarifying text to PUT and POST requests to specify JSON in the body. o Added Editor's Note to DELETE operation about its inclusion. o Added Editor's Note to registration_access_url about alternate syntax proposals. -05 o changed redirect_uri and contact to lists instead of space delimited strings o removed operation parameter o added _links structure o made client update management more RESTful o split endpoint into three parts o changed input to JSON from form-encoded o added READ and DELETE operations o removed Requirements section o changed token_endpoint_auth_type back to token_endpoint_auth_method to match OIDC who changed to match us -04 Richer, et al. Expires September 24, 2015 [Page 38] Internet-Draft OAuth 2.0 Dynamic Registration March 2015 o removed default_acr, too undefined in the general OAuth2 case o removed default_max_auth_age, since there's no mechanism for supplying a non-default max_auth_age in OAuth2 o clarified signing and encryption URLs o changed token_endpoint_auth_method to token_endpoint_auth_type to match OIDC -03 o added scope and grant_type claims o fixed various typos and changed wording for better clarity o endpoint now returns the full set of client information o operations on client_update allow for three actions on metadata: leave existing value, clear existing value, replace existing value with new value -02 o Reorganized contributors and references o Moved OAuth references to RFC o Reorganized model/protocol sections for clarity o Changed terminology to "client register" instead of "client associate" o Specified that client_id must match across all subsequent requests o Fixed RFC2XML formatting, especially on lists -01 o Merged UMA and OpenID Connect registrations into a single document o Changed to form-parameter inputs to endpoint o Removed pull-based registration -00 o Imported original UMA draft specification Authors' Addresses Justin Richer (editor) Email: ietf@justin.richer.org Michael B. Jones Microsoft Email: mbj@microsoft.com URI: http://self-issued.info/ Richer, et al. Expires September 24, 2015 [Page 39] Internet-Draft OAuth 2.0 Dynamic Registration March 2015 John Bradley Ping Identity Email: ve7jtb@ve7jtb.com Maciej Machulak Newcastle University Email: maciej.machulak@gmail.com Phil Hunt Oracle Corporation Email: phil.hunt@yahoo.com Richer, et al. Expires September 24, 2015 [Page 40]