| OAuth Working Group | J. Richer, Ed. |
| Internet-Draft | The MITRE Corporation |
| Intended status: Standards Track | December 6, 2014 |
| Expires: June 9, 2015 |
OAuth 2.0 Token Introspection
draft-ietf-oauth-introspection-03
This specification defines a method for a protected resource to query an OAuth 2.0 authorization server to determine the active state of an OAuth 2.0 token and to determine meta-information about this token. OAuth 2.0 deployments can use this method to convey information about the authorization context of the token from the authorization server to the protected resource.
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 RFC 2119 [RFC2119].
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In OAuth 2.0, the contents of tokens are opaque to clients. This means that the client does not need to know anything about the content or structure of the token itself, if there is any. However, there is still a large amount of metadata that may be attached to a token, such as its current validity, approved scopes, and information about the context in which the token was issued. These pieces of information are often vital to protected resources making authorization decisions based on the tokens being presented. Since OAuth 2.0 [RFC6749] defines no direct relationship between the authorization server and the protected resource, only that they must have an agreement on the tokens themselves, there have been many different approaches to bridging this gap. These include using structured token formats such as JWT [JWT] or proprietary inter-service communication mechanisms (such as shared databases and protected enterprise service buses) that convey token information.
This specification defines an interoperable web API that allows authorized protected resources to query the authorization server to determine the set of metadata for a given token that was presented to them by an OAuth 2.0 client. This metadata includes whether or not the token is currently active (or if it has expired or otherwise been revoked), what rights of access the token carries (usually conveyed through OAuth 2.0 scopes), and the authorization context in which the token was granted (including who authorized the token and which client it was issued to). Token introspection allows a protected resource to query this information regardless of whether or not it is carried in the token itself, allowing this method to be used along with or independently of structured token values. Additionally, a protected resource can use the mechanism described in this specification to introspect the token in a particular authorization decision context and ascertain the relevant metadata about the token in order to make this authorization decision appropriately.
This section defines the terminology used by this specification. This section is a normative portion of this specification, imposing requirements upon implementations.
This specification uses the terms "access token", "authorization endpoint", "authorization grant", "authorization server", "client", "client identifier", "protected resource", "refresh token", "resource owner", "resource server", and "token endpoint" defined by OAuth 2.0 [RFC6749], and the terms "claim names" and "claim values" defined by JSON Web Token (JWT) [JWT].
The introspection endpoint is an OAuth 2.0 endpoint that takes a parameter representing an OAuth 2.0 token and returns a JSON [RFC7159] document representing the meta information surrounding the token, including whether this token is currently active. The definition of an active token is up to the authorization server, but this is commonly a token that has been issued by this authorization server, is not expired, has not been revoked, and is within the purview of the protected resource making the introspection call.
The introspection endpoint MUST be protected by TLS of at least version 1.2 RFC 5246 [RFC5246] and MAY support additional transport-layer mechanisms meeting its security requirements. When using TLS, the protected resource 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 [TLS.BCP].
The protected resource calls the introspection endpoint using an HTTP POST [RFC7231] request with parameters sent as application/x-www-form-urlencoded data as defined in [W3C.REC-html5-20141028]. The authorization server MAY allow an HTTP GET [RFC7231] request with parameters passed in the query string as defined in [W3C.REC-html5-20141028]. The protected resource sends a parameter representing the token along with optional parameters representing additional context that is known by the protected resource to aid the authorization server in its response.
The endpoint MAY allow other parameters to provide further context to the query. For instance, an authorization service may need to know the IP address of the client accessing the protected resource in order to determine the appropriateness of the token being presented.
To prevent unauthorized token scanning attacks, the endpoint MUST also require some form of authorization to access this endpoint, such as client authentication as described in OAuth 2.0 [RFC6749] or a separate OAuth 2.0 access token such as the bearer token described in OAuth 2.0 Bearer Token Usage [RFC6750]. The methods of managing and validating these authentication credentials are out of scope of this specification.
The server responds with a JSON object [RFC7159] in application/json format with the following top-level members. Several of these
The response MAY include any claims defined as JWT [JWT] claim names and carry the same semantics and syntax, such as the following:
Specific implementations MAY extend this structure with their own service-specific pieces of information.
The response MAY be cached by the protected resource.
The authorization server MAY respond differently to different protected resources making the same request.
Note that in order to avoid disclosing too much of the authorization server's state to a third party, the authorization server SHOULD NOT include any additional information about an inactive token, including why the token is inactive.
If the protected resource uses OAuth 2.0 client credentials to authenticate to the introspection endpoint and its credentials are invalid, the authorization server responds with an HTTP 401 (Unauthorized) as described in section 5.2 of OAuth 2.0 [RFC6749].
If the protected resource uses an OAuth 2.0 bearer token to authorize its call to the introspection endpoint and the token used for authorization does not contain sufficient privileges or is otherwise invalid for this request, the authorization server responds with an HTTP 401 code as described in section 3 of OAuth 2.0 Bearer Token Usage [RFC6750].
This specification requests IANA to register the following values into the IANA JSON Web Token Claims registry for JWT Claim Names.
If left unprotected and un-throttled, the introspection endpoint could present a means for an attacker to poll a series of possible token values, fishing for a valid token. To prevent this, the authorization server MUST require authentication of protected resources that need to access the introspection endpoint and SHOULD require protected resources to be specifically authorized to call the introspection endpoint. The specifics of this authentication credentials are out of scope of this specification, but commonly these credentials could take the form of any valid client authentication mechanism used with the token endpoint, an OAuth 2.0 access token, or other HTTP authorization or authentication mechanism. A single piece of software acting as both a client and a protected resource MAY re-use the same credentials between the token endpoint and the introspection endpoint, though doing so potentially conflates the activities of the client and protected resource portions of the software and the authorization server MAY require separate credentials for each mode.
Since the introspection endpoint takes in OAuth 2.0 tokens as parameters, 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 or protected resource 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 [TLS.BCP].
In order to prevent the values of access tokens being from leaking into server-side logs via query parameters, an authorization server offering token introspection MAY disallow HTTP GET and instead require an HTTP POST method only to the introspection endpoint.
In order to avoid disclosing internal server state, an introspection response for an inactive token SHOULD NOT contain any additional claims beyond the required active claim (with its value set to false).
An authorization server offering token introspection MUST be able to understand the token values being presented to it during this call. The exact means by which this happens is an implementation detail and outside the scope of this specification. For unstructured tokens, this could take the form of a simple server-side database query against a data store containing the context information for the token. For structured tokens, this could take the form of the server parsing the token, validating its signature or other protection mechanisms, and returning the information contained in the token back to the protected resource (allowing the protected resource to be unaware of the token's contents, much like the client).
Note that for tokens carrying encrypted information that is needed during the introspection process, the authorization server MUST be able to decrypt and validate the token in order to access this information. Also note that in cases where the authorization server stores no information about the token and has no means of accessing information about the token by parsing the token itself, it can not likely offer an introspection service.
The introspection response may contain privacy-sensitive information such as user identifiers for resource owners. When this is the case, measures MUST be taken to prevent disclosure of this information to unintended parties. One way to limit disclosure is to require authorization to call the introspection endpoint and to limit calls to only registered and trusted protected resource servers. Another method is to transmit user identifiers as opaque service-specific strings, potentially returning different identifiers to each protected resource. Omitting privacy-sensitive information from an introspection response is the simplest way of minimizing privacy issues.
Thanks to the OAuth Working Group and the UMA Working Group for feedback.
| [JWT] | Jones, M., Bradley, J. and N. Sakimura, "JSON Web Token (JWT)", Internet-Draft draft-ietf-oauth-json-web-token, July 2014. |
| [TLS.BCP] | Sheffer, Y., Holz, R. and P. Saint-Andre, "Recommendations for Secure Use of TLS and DTLS", November 2014. |
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In this non-normative example, a protected resource receives a request from a client carrying an OAuth 2.0 bearer token as defined in OAuth 2.0 Bearer Token Usage [RFC6750]. In order to know how and whether to serve the request given this token, the protected resource then makes the following request to the introspection endpoint of the authorization server. The protected resource authenticates with its own credentials, here re-using the format of client identifier and client secret conveyed as HTTP Basic authentication as per OAuth 2.0 [RFC6749] Section 2.3.1.
Following is a non-normative example request:
POST /introspect HTTP/1.1 Host: authserver.example.com Content-type: application/x-www-form-urlencoded Accept: application/json Authorization: Basic czZCaGRSa3F0Mzo3RmpmcDBaQnIxS3REUmJuZlZkbUl3 token=X3241Affw.4233-99JXJ
In this non-normative example, the protected resource also sends a resource identifier and token type hint to the authorization server to aid the authorization server's response:
Following is a non-normative example request (with line wraps for display purposes only):
POST /introspect HTTP/1.1 Host: authserver.example.com Content-type: application/x-www-form-urlencoded Accept: application/json Authorization: Basic czZCaGRSa3F0Mzo3RmpmcDBaQnIxS3REUmJuZlZkbUl3 token=X3241Affw.4233-99JXJ &resource_id=rsid-2348e.2381k3 &token_type_hint=access_token
The authorization server validates the protected resource's credentials and looks up the information in the token. If the token is currently active and the authenticated protected resource is authorized to know information about this token, the authorization server returns the following JSON document.
Following is a non-normative example active token response (with line wraps for display purposes only):
HTTP/1.1 200 OK
Content-Type: application/json
{
"active": true,
"client_id":"s6BhdRkqt3",
"scope": "read write dolphin",
"sub": "2309fj32kl",
"user_id": "jdoe",
"aud": "https://example.org/protected-resource/*",
"iss": "https://authserver.example.com/"
}
If the token presented is not currently active for any reason (for instance, it has been revoked by the resource owner, it has expired, or the protected resource is not allowed to ask about this particular token) but the authorization presented during the request is otherwise valid, the authorization server returns the following JSON document.
Following is a non-normative example response to an inactive or invalid token (with line wraps for display purposes only):
HTTP/1.1 200 OK
Content-Type: application/json
{
"active": false
}
With bearer tokens such as those defined by OAuth 2.0 Bearer Token Usage [RFC6750], the protected resource will have in its possession the entire secret portion of the token for submission to the introspection service. However, for proof-of-possession style tokens, the protected resource will have only a token identifier used during the request, along with the cryptographic signature on the request. The protected resource would be able to submit the token identifier to the authorization server's token endpoint in order to obtain the necessary key information needed to validate the signature on the request. The details of this usage are outside the scope of this specification and should be defined in an extension to this specification.