| OAuth Working Group | M. Jones |
| Internet-Draft | Microsoft |
| Intended status: Standards Track | N. Sakimura |
| Expires: September 5, 2018 | NRI |
| J. Bradley | |
| Ping Identity | |
| March 4, 2018 |
OAuth 2.0 Authorization Server Metadata
draft-ietf-oauth-discovery-10
This specification defines a metadata format that an OAuth 2.0 client can use to obtain the information needed to interact with an OAuth 2.0 authorization server, including its endpoint locations and authorization server capabilities.
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 https://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 5, 2018.
Copyright (c) 2018 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 (https://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.
This specification generalizes the metadata format defined by "OpenID Connect Discovery 1.0" in a way that is compatible with OpenID Connect Discovery, while being applicable to a wider set of OAuth 2.0 use cases. This is intentionally parallel to the way that the "OAuth 2.0 Dynamic Client Registration Protocol" specification generalized the dynamic client registration mechanisms defined by "OpenID Connect Dynamic Client Registration 1.0" in a way that was compatible with it.
The metadata for an authorization server is retrieved from a well-known location as a JSON [RFC7159] document, which declares its endpoint locations and authorization server capabilities. This process is described in Section 3.
This metadata can either be communicated in a self-asserted fashion by the server origin via HTTPS or as a set of signed metadata values represented as claims in a JSON Web Token (JWT) [JWT]. In the JWT case, the issuer is vouching for the validity of the data about the authorization server. This is analogous to the role that the Software Statement plays in OAuth Dynamic Client Registration [RFC7591].
The means by which the client chooses an authorization server is out of scope. In some cases, its issuer identifier may be manually configured into the client. In other cases, it may be dynamically discovered, for instance, through the use of WebFinger, as described in Section 2 of "OpenID Connect Discovery 1.0".
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.
All uses of JSON Web Signature (JWS) and JSON Web Encryption (JWE) data structures in this specification utilize the JWS Compact Serialization or the JWE Compact Serialization; the JWS JSON Serialization and the JWE JSON Serialization are not used.
This specification uses the terms "Access Token", "Authorization Code", "Authorization Endpoint", "Authorization Grant", "Authorization Server", "Client", "Client Authentication", "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, the terms "Claim Name", "Claim Value", and "JSON Web Token (JWT)" defined by JSON Web Token (JWT), and the term "Response Mode" defined by OAuth 2.0 Multiple Response Type Encoding Practices.
Authorization servers can have metadata describing their configuration. The following authorization server metadata values are used by this specification and are registered in the IANA "OAuth Authorization Server Metadata" registry established in Section 7.1:
Additional authorization server metadata parameters MAY also be used. Some are defined by other specifications, such as OpenID Connect Discovery 1.0.
In addition to JSON elements, metadata values MAY also be provided as a signed_metadata value, which is a JSON Web Token (JWT) [JWT] that asserts metadata values about the authorization server as a bundle. A set of claims that can be used in signed metadata are defined in Section 2. The signed metadata MUST be digitally signed or MACed using JSON Web Signature (JWS) and MUST contain an iss (issuer) claim denoting the party attesting to the claims in the signed metadata. Consumers of the metadata MAY ignore the signed metadata if they do not support this feature. If the consumer of the metadata supports signed metadata, metadata values conveyed in the signed metadata MUST take precedence over the corresponding values conveyed using plain JSON elements.
Signed metadata is included in the authorization server metadata JSON object using this OPTIONAL member:
Authorization servers supporting metadata MUST make a JSON document containing metadata as specified in Section 2 available at a path formed by inserting a well-known URI string into the authorization server's issuer identifier between the host component and the path component, if any. By default, the well-known URI string used is /.well-known/oauth-authorization-server. This path MUST use the https scheme. The syntax and semantics of .well-known are defined in RFC 5785. The well-known URI suffix used MUST be registered in the IANA "Well-Known URIs" registry [IANA.well-known].
Different applications utilizing OAuth authorization servers in application-specific ways may define and register different well-known URI suffixes used to publish authorization server metadata as used by those applications. For instance, if the Example application uses an OAuth authorization server in an Example-specific way, and there are Example-specific metadata values that it needs to publish, then it might register and use the example-configuration URI suffix and publish the metadata document at the path formed by inserting /.well-known/example-configuration between the host and path components of the authorization server's issuer identifier. Alternatively, many such applications will use the default well-known URI string /.well-known/oauth-authorization-server, which is the right choice for general-purpose OAuth authorization servers, and not register an application-specific one.
An OAuth 2.0 application using this specification MUST specify what well-known URI suffix it will use for this purpose. The same authorization server MAY choose to publish its metadata at multiple well-known locations derived from its issuer identifier, for example, publishing metadata at both /.well-known/example-configuration and /.well-known/oauth-authorization-server.
Some OAuth applications will choose to use the well-known URI suffix openid-configuration. As described in Section 5, despite the identifier /.well-known/openid-configuration, appearing to be OpenID-specific, its usage in this specification is actually referring to a general OAuth 2.0 feature that is not specific to OpenID Connect.
An authorization server metadata document MUST be queried using an HTTP GET request at the previously specified path.
The client would make the following request when the issuer identifier is https://example.com and the well-known URI suffix is oauth-authorization-server to obtain the metadata, since the issuer identifier contains no path component:
GET /.well-known/oauth-authorization-server HTTP/1.1 Host: example.com
If the issuer identifier value contains a path component, any terminating / MUST be removed before inserting /.well-known/ and the well-known URI suffix between the host component and the path component. The client would make the following request when the issuer identifier is https://example.com/issuer1 and the well-known URI suffix is oauth-authorization-server to obtain the metadata, since the issuer identifier contains a path component:
GET /.well-known/oauth-authorization-server/issuer1 HTTP/1.1 Host: example.com
Using path components enables supporting multiple issuers per host. This is required in some multi-tenant hosting configurations. This use of .well-known is for supporting multiple issuers per host; unlike its use in RFC 5785, it does not provide general information about the host.
The response is a set of claims about the authorization server's configuration, including all necessary endpoints and public key location information. A successful response MUST use the 200 OK HTTP status code and return a JSON object using the application/json content type that contains a set of claims as its members that are a subset of the metadata values defined in Section 2. Other claims MAY also be returned.
Claims that return multiple values are represented as JSON arrays. Claims with zero elements MUST be omitted from the response.
An error response uses the applicable HTTP status code value.
The following is a non-normative example response:
HTTP/1.1 200 OK
Content-Type: application/json
{
"issuer":
"https://server.example.com",
"authorization_endpoint":
"https://server.example.com/authorize",
"token_endpoint":
"https://server.example.com/token",
"token_endpoint_auth_methods_supported":
["client_secret_basic", "private_key_jwt"],
"token_endpoint_auth_signing_alg_values_supported":
["RS256", "ES256"],
"userinfo_endpoint":
"https://server.example.com/userinfo",
"jwks_uri":
"https://server.example.com/jwks.json",
"registration_endpoint":
"https://server.example.com/register",
"scopes_supported":
["openid", "profile", "email", "address",
"phone", "offline_access"],
"response_types_supported":
["code", "code token"],
"service_documentation":
"http://server.example.com/service_documentation.html",
"ui_locales_supported":
["en-US", "en-GB", "en-CA", "fr-FR", "fr-CA"]
}
The issuer value returned MUST be identical to the authorization server's issuer identifier value into which the well-known URI string was inserted to create the URL used to retrieve the metadata. If these values are not identical, the data contained in the response MUST NOT be used.
Processing some OAuth 2.0 messages requires comparing values in the messages to known values. For example, the member names in the metadata response might be compared to specific member names such as issuer. Comparing Unicode [UNICODE] strings, however, has significant security implications.
Therefore, comparisons between JSON strings and other Unicode strings MUST be performed as specified below:
Note that this is the same equality comparison procedure described in Section 8.3 of [RFC7159].
The identifiers /.well-known/openid-configuration, op_policy_uri, and op_tos_uri contain strings referring to the OpenID Connect [OpenID.Core] family of specifications that were originally defined by "OpenID Connect Discovery 1.0". Despite the reuse of these identifiers that appear to be OpenID-specific, their usage in this specification is actually referring to general OAuth 2.0 features that are not specific to OpenID Connect.
The algorithm for transforming the issuer identifier to an authorization server metadata location defined in Section 3 is equivalent to the corresponding transformation defined in Section 4 of "OpenID Connect Discovery 1.0", provided that the issuer identifier contains no path component. However, they are different when there is a path component, because OpenID Connect Discovery 1.0 specifies that the well-known URI string is appended to the issuer identifier (e.g., https://example.com/issuer1/.well-known/openid-configuration), whereas this specification specifies that the well-known URI string is inserted before the path component of the issuer identifier (e.g., https://example.com/.well-known/openid-configuration/issuer1).
Going forward, OAuth authorization server metadata locations should use the transformation defined in this specification. However, when deployed in legacy environments in which the OpenID Connect Discovery 1.0 transformation is already used, it may be necessary during a transition period to publish metadata for issuer identifiers containing a path component at both locations. During this transition period, applications should first apply the transformation defined in this specification and attempt to retrieve the authorization server metadata from the resulting location; only if the retrieval from that location fails should they fall back to attempting to retrive it from the alternate location obtained using the transformation defined by OpenID Connect Discovery 1.0. This backwards-compatibility behavior should only be necessary when the well-known URI suffix employed by the application is openid-configuration.
Implementations MUST support TLS. Which version(s) ought to be implemented will vary over time and depend on the widespread deployment and known security vulnerabilities at the time of implementation. The authorization server MUST support TLS version 1.2 [RFC5246] and MAY support additional transport-layer security mechanisms meeting its security requirements. When using TLS, the client MUST perform a TLS/SSL server certificate check, per RFC 6125. Implementation security considerations can be found in Recommendations for Secure Use of TLS and DTLS.
To protect against information disclosure and tampering, confidentiality protection MUST be applied using TLS with a ciphersuite that provides confidentiality and integrity protection.
TLS certificate checking MUST be performed by the client, as described in Section 6.1, when making an authorization server metadata request. Checking that the server certificate is valid for the issuer identifier URL prevents man-in-middle and DNS-based attacks. These attacks could cause a client to be tricked into using an attacker's keys and endpoints, which would enable impersonation of the legitimate authorization server. If an attacker can accomplish this, they can access the resources that the affected client has access to using the authorization server that they are impersonating.
An attacker may also attempt to impersonate an authorization server by publishing a metadata document that contains an issuer claim using the issuer identifier URL of the authorization server being impersonated, but with its own endpoints and signing keys. This would enable it to impersonate that authorization server, if accepted by the client. To prevent this, the client MUST ensure that the issuer identifier URL it is using as the prefix for the metadata request exactly matches the value of the issuer metadata value in the authorization server metadata document received by the client.
Publishing information about the authorization server in a standard format makes it easier for both legitimate clients and attackers to use the authorization server. Whether an authorization server publishes its metadata in an ad-hoc manner or in the standard format defined by this specification, the same defenses against attacks that might be mounted that use this information should be applied.
Secure determination of appropriate protected resources to use with an authorization server for all use cases is out of scope of this specification. This specification assumes that the client has a means of determining appropriate protected resources to use with an authorization server and that the client is using the correct metadata for each authorization server. Implementers need to be aware that if an inappropriate protected resource is used by the client, that an attacker may be able to act as a man-in-the-middle proxy to a valid protected resource without it being detected by the authorization server or the client.
The ways to determine the appropriate protected resources to use with an authorization server are in general, application-dependent. For instance, some authorization servers are used with a fixed protected resource or set of protected resources, the locations of which may be well known, or which could be published as metadata values by the authorization server. In other cases, the set of resources that can be used with an authorization server can by dynamically changed by administrative actions. Many other means of determining appropriate associations between authorization servers and protected resources are also possible.
The following registration procedure is used for the registry established by this specification.
Values are registered on a Specification Required [RFC8126] basis 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 Experts may approve registration once they are satisfied that such a specification will be published.
Registration requests sent to the mailing list for review should use an appropriate subject (e.g., "Request to register OAuth Authorization Server Metadata: example").
Within the review period, the Designated Experts 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. Registration requests that are undetermined for a period longer than 21 days can be brought to the IESG's attention (using the iesg@ietf.org mailing list) for resolution.
Criteria that should be applied by the Designated Experts includes determining whether the proposed registration duplicates existing functionality, determining whether it is likely to be of general applicability or whether it is useful only for a single application, and whether the registration makes sense.
IANA must only accept registry updates from the Designated Experts and should direct all requests for registration to the review mailing list.
It is suggested that multiple Designated Experts be appointed who are able to represent the perspectives of different applications using this specification, in order to enable broadly-informed review of registration decisions. In cases where a registration decision could be perceived as creating a conflict of interest for a particular Expert, that Expert should defer to the judgment of the other Experts.
This specification establishes the IANA "OAuth Authorization Server Metadata" registry for OAuth 2.0 authorization server metadata names. The registry records the authorization server metadata member and a reference to the specification that defines it.
The Designated Experts must either:
(a) require that metadata names and values being registered use only printable ASCII characters excluding double quote ('"') and backslash ('\') (the Unicode characters with code points U+0021, U+0023 through U+005B, and U+005D through U+007E), or
(b) if new metadata members or values are defined that use other code points, require that their definitions specify the exact Unicode code point sequences used to represent them. Furthermore, proposed registrations that use Unicode code points that can only be represented in JSON strings as escaped characters must not be accepted.
This specification adds to the instructions for the Designated Experts of the following IANA registries, both of which are in the "OAuth Parameters" registry [IANA.OAuth.Parameters]:
IANA has added a link to this specification in the Reference sections of these registries. [[ RFC Editor: The above sentence is written in the past tense as it would appear in the final specification, even though these links won't actually be created until after the IESG has requested publication of the specification. Please delete this note after the links are in place. ]]
For these registries, the designated experts must reject registration requests in one registry for values already occurring in the other registry. This is necessary because the introspection_endpoint_auth_methods_supported parameter allows for the use of values from either registry. That way, because the values in the two registries will continue to be mutually exclusive, no ambiguities will arise.
This specification registers the well-known URI defined in Section 3 in the IANA "Well-Known URIs" registry [IANA.well-known] established by RFC 5785.
| [I-D.ietf-oauth-mix-up-mitigation] | Jones, M., Bradley, J. and N. Sakimura, "OAuth 2.0 Mix-Up Mitigation", Internet-Draft draft-ietf-oauth-mix-up-mitigation-01, July 2016. |
| [IANA.well-known] | IANA, "Well-Known URIs" |
| [OpenID.Core] | Sakimura, N., Bradley, J., Jones, M., de Medeiros, B. and C. Mortimore, "OpenID Connect Core 1.0", November 2014. |
| [OpenID.Discovery] | Sakimura, N., Bradley, J., Jones, M. and E. Jay, "OpenID Connect Discovery 1.0", November 2014. |
| [OpenID.Registration] | Sakimura, N., Bradley, J. and M. Jones, "OpenID Connect Dynamic Client Registration 1.0", November 2014. |
This specification is based on the OpenID Connect Discovery 1.0 specification, which was produced by the OpenID Connect working group of the OpenID Foundation. This specification standardizes the de facto usage of the metadata format defined by OpenID Connect Discovery to publish OAuth authorization server metadata.
The authors would like to thank the following people for their reviews of this specification: Shwetha Bhandari, Ben Campbell, Brian Campbell, Brian Carpenter, William Denniss, Vladimir Dzhuvinov, Donald Eastlake, Samuel Erdtman, George Fletcher, Dick Hardt, Phil Hunt, Alexey Melnikov, Tony Nadalin, Mark Nottingham, Eric Rescorla, Justin Richer, Adam Roach, Hannes Tschofenig, and Hans Zandbelt.
[[ to be removed by the RFC Editor before publication as an RFC ]]
-10
-09
-08
-07
-06
-05
-04
-03
-02
-01
-00