Support RFC 8693 token exchange for enterprise IdP flows (SEP-990) (#2988)

Co-authored-by: Max Isbey <224885523+maxisbey@users.noreply.github.com>

examples/snippets/clients/identity_assertion_client.py

@@ -0,0 +1,82 @@
+"""Client side of SEP-990 (enterprise IdP policy controls).
+
+`IdentityAssertionOAuthProvider` presents an Identity Assertion Authorization Grant (ID-JAG) issued
+by the enterprise IdP to the MCP authorization server using the RFC 7523 jwt-bearer grant
+(`grant_type=urn:ietf:params:oauth:grant-type:jwt-bearer`, ID-JAG as `assertion`), and receives an
+MCP access token. No browser redirect or dynamic client registration is involved.
+
+Obtaining the ID-JAG (logging into the IdP and the leg-1 exchange against it) is deployment-specific
+and out of scope for the SDK; supply it through the `assertion_provider` callback. The callback
+receives the authorization server's issuer (the ID-JAG `aud`) and the MCP server's resource
+identifier (the ID-JAG `resource` claim). SEP-990 requires a confidential client, so a client secret
+is mandatory, and `issuer` is the authorization server the credentials are provisioned for - the
+provider fetches metadata from that issuer's well-known and never asks the resource server which AS
+to use.
+"""
+
+import asyncio
+
+import httpx
+
+from mcp import ClientSession
+from mcp.client.auth.extensions.identity_assertion import IdentityAssertionOAuthProvider
+from mcp.client.streamable_http import streamable_http_client
+from mcp.shared.auth import OAuthClientInformationFull, OAuthToken
+
+
+class InMemoryTokenStorage:
+    """Demo in-memory token storage."""
+
+    def __init__(self) -> None:
+        self.tokens: OAuthToken | None = None
+        self.client_info: OAuthClientInformationFull | None = None
+
+    async def get_tokens(self) -> OAuthToken | None:
+        return self.tokens
+
+    async def set_tokens(self, tokens: OAuthToken) -> None:
+        self.tokens = tokens
+
+    async def get_client_info(self) -> OAuthClientInformationFull | None:
+        return self.client_info
+
+    async def set_client_info(self, client_info: OAuthClientInformationFull) -> None:
+        self.client_info = client_info
+
+
+async def fetch_id_jag(audience: str, resource: str) -> str:
+    """Return the ID-JAG to present.
+
+    `audience` is the MCP authorization server's issuer (the ID-JAG `aud` claim); `resource` is the
+    MCP server's RFC 9728 identifier (the ID-JAG `resource` claim, which the AS audience-restricts
+    the issued token against). In production this exchanges the user's IdP ID token for an ID-JAG
+    against the enterprise identity provider.
+    """
+    raise NotImplementedError("Obtain the ID-JAG from your enterprise identity provider")
+
+
+async def main() -> None:
+    oauth_auth = IdentityAssertionOAuthProvider(
+        server_url="http://localhost:8001/mcp",
+        storage=InMemoryTokenStorage(),
+        client_id="enterprise-mcp-client",
+        client_secret="enterprise-mcp-secret",
+        issuer="http://localhost:8001",
+        assertion_provider=fetch_id_jag,
+        scope="user",
+    )
+
+    async with httpx.AsyncClient(auth=oauth_auth, follow_redirects=True) as http_client:
+        async with streamable_http_client("http://localhost:8001/mcp", http_client=http_client) as (read, write):
+            async with ClientSession(read, write) as session:
+                await session.initialize()
+                tools = await session.list_tools()
+                print(f"Available tools: {[tool.name for tool in tools.tools]}")
+
+
+def run() -> None:
+    asyncio.run(main())
+
+
+if __name__ == "__main__":
+    run()