Enterprise-Managed Authorization

Protocol Revision: draft

1. Introduction

1.1 Purpose and Scope

This document defines an application of the “Identity Assertion Authorization Grant” for use within enterprise deployments of the Model Context Protocol (MCP).

When an MCP Client and MCP Server are both enabled for single sign-on through an enterprise Identity Provider, this three-way relationship can be leveraged to streamline the authorization process.

This document specifies how an MCP Client can obtain an access token from an MCP Server’s Authorization Server by presenting an identity assertion it previously obtained from an enterprise Identity Provider during single sign-on. It also describes how an MCP Server’s Authorization Server can validate the request from the client before issuing an access token.

This profile is designed to facilitate secure and interoperable authorization within enterprise environments, leveraging the organization’s existing identity infrastructure. Enterprise-managed authorization for MCP Clients and Servers has two key benefits:

• For end users, this removes the need to manually connect and authorize the MCP Client to each MCP Server for use within the organization.
• For enterprise admins, this enables visibility and control over which MCP Servers are able to be used within the organization.

1.2 Roles and Terminology

• Resource Application: In the context of this profile, the Resource Application is the MCP Server.
• Identity Provider (IdP): An entity that creates, maintains, and manages identity information, provides authentication services, and is trusted by a set of applications in an organization’s app ecosystem.
• Identity Assertion: A security token (e.g., ID Token, SAML Assertion) that contains information about an authenticated user and is issued by an Identity Provider trusted by the Authorization Server.
• Authorization Server: This profile uses the term “Authorization Server” to refer to the authorization server that issues tokens to be used at the MCP server.
• Client: In the context of this profile, the Client is the MCP Client.
• ID Token: A security token that contains claims about the authentication of a user when using a client, as defined in OpenID Connect.
• Subject Token: A security token that represents the identity of the user, such as an ID Token.
• JAG: JWT Authorization Grant, as described in RFC7523.

2. Identity Assertion Authorization Grant Overview

This profile is an application of the “Identity Assertion Authorization Grant” draft-ietf-oauth-identity-assertion-authz-grant, which itself is a profile of “Identity and Authorization Chaining Across Domains” draft-ietf-oauth-identity-chaining.

The Identity Assertion Authorization Grant follows three steps:

1. Single Sign-On to the MCP Client via OpenID Connect or SAML
2. Token Exchange (RFC8623)
3. JWT Authorization Grant (RFC7523)

The core flow is as follows:

• A user logs in to an MCP Client through their enterprise Identity Provider, resulting in an Identity Assertion (ID Token or SAML assertion) being issued to the MCP Client.
• The MCP Client sends a Token Exchange [RFC8693] request to the Identity Provider including the identity assertion and identifier of the MCP Server it is attempting to access, and obtains a Identity Assertion JWT Authorization Grant (ID-JAG).
• The MCP Client uses the Identity Assertion JWT Authorization Grant as a JWT Authorization Grant [RFC7523] to request an access token from the Authorization Server.
• The Authorization Server validates the Identity Assertion Authorization Grant and, if valid, issues an access token.
• The MCP Client uses the access token to make requests to the MCP Server.

2.1 Sequence Diagram

The following diagram outlines an example flow:

3. User Authentication

To authenticate a user, the MCP Client initiates the process through a request with the IdP using OpenID Connect or SAML.

For example, a web-based MCP client might initiate the user authentication process by redirecting the browser using OpenID Connect:

302 Redirect
Location: https://acme.idp.example/authorize?response_type=code&scope=openid&client_id=...

The user authenticates with the IdP, and is redirected back to the Client with an authorization code, which it can then exchange for an ID Token.

The enterprise IdP may enforce additional security controls such as multi-factor authentication before granting the user access to the MCP Client. For example, in an OpenID Connect flow, after receiving a redirect from the IdP with an authorization code, the MCP server makes a request to the Authorization Server and, if valid, receives the tokens in the response:

POST /token HTTP/1.1
Host: acme.idp.example
Content-Type: application/x-www-form-urlencoded

grant_type=authorization_code
&code=.....

HTTP/1.1 200 OK
Content-Type: application/json

{
  "id_token": "eyJraWQiOiJzMTZ0cVNtODhwREo4VGZCXzdrSEtQ...",
  "token_type": "Bearer",
  "access_token": "7SliwCQP1brGdjBtsaMnXo",
  "scope": "openid"
}

4. Token Exchange

To request a JWT Assertion Grant, the MCP Client MUST make a Token Exchange (RFC8693) request to the IdP’s Token Endpoint with the following parameters:

Parameter	Required/Optional	Description	Example/Allowed Values
requested_token_type	REQUIRED	Indicates that an ID Assertion JWT is being requested.	urn:ietf:params:oauth:token-type:id-jag
audience	REQUIRED	The Issuer URL of the MCP server’s authorization server.	https://auth.chat.example/
resource	REQUIRED	The RFC9728 Resource Identifier of the MCP server.	https://mcp.chat.example/
scope	OPTIONAL	The space-separated list of scopes at the MCP Server that are being requested.	scope1 scope2
subject_token	REQUIRED	The identity assertion (e.g. the OpenID Connect ID Token or SAML assertion) for the target end-user.	(JWT or SAML assertion string)
subject_token_type	REQUIRED	Indicates the type of the security token in the subject_token parameter, as specified in RFC8693 Section 3.	urn:ietf:params:oauth:token-type:id_token (OIDC) urn:ietf:params:oauth:token-type:saml2 (SAML)

Additional parameters defined in Section 2.1 of RFC8693 (actor_token and actor_token_type) are not used in this specification.

If the IdP requires client authentication when the MCP Client performs OpenID Connect for single sign-on, then client authentication of the Token Exchange request is also required.

The example below illustrates the Token Exchange request, using an OpenID Connect ID Token as the Identity Assertion and a client secret as the client authentication method. The ID token is passed as a Subject Token.

POST /oauth2/token HTTP/1.1
Host: acme.idp.example
Content-Type: application/x-www-form-urlencoded

grant_type=urn:ietf:params:oauth:grant-type:token-exchange
&requested_token_type=urn:ietf:params:oauth:token-type:id-jag
&audience=https://auth.chat.example/
&resource=https://mcp.chat.example/
&scope=chat.read+chat.history
&subject_token=eyJraWQiOiJzMTZ0cVNtODhwREo4VGZCXzdrSEtQ...
&subject_token_type=urn:ietf:params:oauth:token-type:id_token
&client_id=2ec954a1d60620116d36d9ceb7
&client_secret=a26d84873504215a34a86d52ef5cd64f4b76

4.1 Processing Rules

The IdP MUST validate the Subject Token, and MUST validate that the audience of the Subject Token (e.g. the aud claim of the ID Token) matches the Client Identifier of the MCP client making this request (e.g. by checking the client_id in the client authentication).

The IdP evaluates administrator-defined policies for the token exchange request and determines if the MCP Client should be granted access to act on behalf of the user for the target MCP Server and scopes.

The IdP may also introspect the authentication context described in the Identity Assertion to determine if step-up authentication is required.

4.2 Token Exchange Response

If access is granted, the IdP creates a signed Identity Assertion JWT Authorization Grant and returns it in the token exchange response defined in Section 2.2 of RFC8693:

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

{
  "issued_token_type": "urn:ietf:params:oauth:token-type:id-jag",
  "access_token": "eyJhbGciOiJIUzI1NiIsI...",
  "token_type": "N_A",
  "scope": "chat.read chat.history",
  "expires_in": 300
}

Parameter	Required/Optional	Description	Example/Allowed Values
issued_token_type	REQUIRED	Indicates the type of token issued.	urn:ietf:params:oauth:token-type:id-jag
access_token	REQUIRED	The Identity Assertion JWT Authorization Grant. (Note: Token Exchange requires the access_token response parameter for historical reasons, not an OAuth token.)	(JWT string)
token_type	REQUIRED	The token type.	N_A (because this is not an OAuth access token.)
scope	OPTIONAL/REQUIRED	OPTIONAL if the scope of the issued token is identical to the requested; otherwise REQUIRED. May be fewer scopes than requested.	scope1 scope2
expires_in	RECOMMENDED	The lifetime in seconds of the authorization grant.	3600

4.2.1 Error Response

In case of an error occurring while performing the token exchange, the IdP will return an OAuth 2.0 Token Error response as defined in Section 5.2 of RFC6749. An example response may look like this:

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

{
  "error": "invalid_grant",
  "error_description": "Audience validation failed"
}

4.3 Identity Assertion JWT Authorization Grant

The Identity Assertion JWT Authorization Grant (ID-JAG) is issued and signed by the IdP, and describes the intended audience of the authorization grant as well as the client to which it was issued and the subject identifier of the resource owner, using the following claims:

Parameter	Required/Optional	Description	Reference / Example
iss	REQUIRED	The IdP issuer URL.	Section 4.1.1 of RFC7519
sub	REQUIRED	The subject identifier (e.g., user ID) of the user at the MCP Server.	Section 4.1.2 of RFC7519
aud	REQUIRED	The Issuer URL of the MCP Server’s authorization server.	Section 4.1.3 of RFC7519
resource	REQUIRED	The Resource Identifier of the MCP Server.	Section 1.2 of RFC9728
client_id	REQUIRED	An identifier of the MCP Client registered at the Authorization Server that this JWT was issued to; SHOULD be a client_id as defined in Section 4.3 of RFC8693.	Section 4.3 of RFC8693
jti	REQUIRED	Unique ID of this JWT.	Section 4.1.7 of RFC7519
exp	REQUIRED	Expiration time of this JWT (Unix timestamp in seconds).	Section 4.1.4 of RFC7519
iat	REQUIRED	Issued-at time of this JWT (Unix timestamp in seconds).	Section 4.1.6 of RFC7519
scope	OPTIONAL	A JSON string containing a space-separated list of scopes associated with the token, per Section 3.3 of RFC6749.	["scope1 scope2"] Section 3.3 of RFC6749

The typ claim of the JWT indicated in the JWT header MUST be oauth-id-jag+jwt.

An example JWT shown with expanded header and payload claims may look like this:

{
  "typ": "oauth-id-jag+jwt"
}
.
{
  "jti": "9e43f81b64a33f20116179",
  "iss": "https://acme.idp.example",
  "sub": "U019488227",
  "aud": "https://auth.chat.example/",
  "resource": "https://mcp.chat.example/",
  "client_id": "f53f191f9311af35",
  "exp": 1311281970,
  "iat": 1311280970,
  "scope": "chat.read chat.history"
}
.
signature

The authorization server MAY add additional claims as necessary.

Implementation notes

If the IdP is multi-tenant and uses the same issuer for all tenants, the MCP Server will already have IdP-specific logic to determine the tenant from the OpenID Connect ID Token (e.g., the hd claim for Google) or SAML assertion, and will need to use that if the IdP also has only one client registration for the MCP Server.

sub should be an opaque ID, as iss+sub is unique. The IdP might want to also include additional user information, such as an email address, which it should do as a new email claim. This may allow the MCP Client application to properly link existing user accounts to the sub identifier used within the enterprise context for SSO.

5. Access Token Request

The MCP Client makes an access token request to the MCP Server’s authorization server using the previously obtained Identity Assertion Authorization Grant as a JWT Assertion as defined by RFC7523.

Parameter	Required/Optional	Description	Example/Allowed Values
grant_type	REQUIRED	MUST be urn:ietf:params:oauth:grant-type:jwt-bearer	urn:ietf:params:oauth:grant-type:jwt-bearer Section 4.1 of RFC7523
assertion	REQUIRED	The Identity Assertion JWT Authorization Grant obtained in the previous token exchange step	(JWT string)

The MCP Client authenticates with its credentials as registered with the MCP Server’s authorization server.

If the MCP Client has not yet registered with the MCP Server’s authorization server, then it can do a Dynamic Client Registration request at this stage.

An example request may look like this:

POST /oauth2/token HTTP/1.1
Host: auth.chat.example
Authorization: Basic yZS1yYW5kb20tc2VjcmV0v3JOkF0XG5Qx2

grant_type=urn:ietf:params:oauth:grant-type:jwt-bearer
assertion=eyJhbGciOiJIUzI1NiIsI...

5.1 Processing Rules

All of Section 5.2 of RFC7521 applies, in addition to the following processing rules:

• Validate the JWT typ is oauth-id-jag+jwt (per RFC8725)
• The aud claim of the assertion JWT MUST identify the Issuer URL of the MCP Server’s authorization server as the intended audience of the JWT.
• The client_id claim of the assertion JWT MUST identify the same client as the client authentication in the request (e.g., the client_id specified in a basic auth header).

5.2 Access Token Response

The MCP Server’s authorization server responds with an OAuth 2.0 Token Response, like this:

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

{
  "token_type": "Bearer",
  "access_token": "2YotnFZFEjr1zCsicMWpAA",
  "expires_in": 86400,
  "scope": "chat.read chat.history"
}

6. Security Considerations

6.1 Client Registration

In most enterprise deployments, the IdP policy will only allow users to sign in to pre-registered clients. The MCP client will likely need to be pre-registered with the enterprise IdP for single sign-on.

It is also assumed that the MCP client will be pre-registered with the MCP server’s authorization server.

In order for the IdP to include the correct client_id in the ID-JAG (described in Section 4.3), the IdP will need to be aware of the MCP Client’s client_id that it normally uses with the MCP Server. This mapping happens outside of the protocol, such as during the configuration of the feature in the IdP.

6.2 Scope of Enterprise Visibility and Policy Enforcement

This specification enables the enterprise IdP to be part of the issuance of the access token at the MCP Server. The visibility the IdP has between the MCP Client and MCP Server is limited to the process of issuing the access token, but does not extend to the actual API calls between the MCP Client and Server.

This enables the enterprise IdP to enforce policies such as which users in the organization can use certain MCP clients with certain MCP servers. Depending on the granularity of the OAuth scopes defined at the MCP server, this can also extend to govern which scopes a given user can request.

For example, the enterprise policy of granting an access token through this extension may allow users in the “engineering” group to get read-only access from an AI code editor to the source control MCP server, whereas users in the “marketing” group may be able to get read and write access to the internal documentation application.