bearer-auth

Resource-server-only bearer auth. Pass a TokenVerifier + AuthSettings (issuer, resource URL, required scopes) when building the streamable-HTTP app and the SDK wires three things automatically: a bearer gate that answers 401 + WWW-Authenticate: Bearer ... resource_metadata=... (or 403 insufficient_scope), the RFC 9728 protected-resource-metadata document at /.well-known/oauth-protected-resource/mcp, and the verified AccessToken inside tool handlers via get_access_token(). The verifier here accepts one static token — replace it with JWT verification or RFC 7662 introspection. No authorization server; see ../oauth/ for the full grant flow.

Run it

# HTTP — the client self-hosts the bearer-gated app, connects with the demo
# bearer token, then tears it down. Self-hosting uses this story's fixed :8000
# (the issuer/PRM metadata pin it), so :8000 must be free.
uv run python -m stories.bearer_auth.client --http
# same, against the lowlevel-API server variant
uv run python -m stories.bearer_auth.client --http --server server_lowlevel

# against a server you run yourself (real uvicorn on :8000). The next section's
# curl probes use it too and `kill` it when done. While it is up it owns :8000,
# so the two self-host lines above refuse to run rather than test it by mistake.
uv run python -m stories.bearer_auth.server --port 8000 &
SERVER_PID=$!
uv run python -m stories.bearer_auth.client --http http://127.0.0.1:8000/mcp

Client(url) has no auth= passthrough, so a target built from a bare URL can't carry the token. Both runners close that gap the same way: run_client (above) and the pytest harness thread the module's build_auth export onto the httpx.AsyncClient underneath the transport and hand main a target that is already routed through it.

Try it without the SDK client

# no token → 401 + WWW-Authenticate pointing at the PRM document
curl -i -X POST http://127.0.0.1:8000/mcp \
  -H 'content-type: application/json' -H 'accept: application/json, text/event-stream' \
  -d '{"jsonrpc":"2.0","id":1,"method":"ping"}'

# the RFC 9728 protected-resource-metadata document
curl -s http://127.0.0.1:8000/.well-known/oauth-protected-resource/mcp | jq

# done with the server you started in "Run it"
kill "$SERVER_PID"

What to look at

• client.py main — opens with async with Client(target, mode=mode) as client: and that is the whole program. The target it receives is a transport that already carries the bearer token; nothing in the body knows auth exists.
• client.py build_auth / StaticBearerAuth — bearer auth client-side is five lines of httpx.Auth. Client(url, auth=...) is the ergonomic the SDK is missing; until it lands, the auth has to be threaded onto the httpx.AsyncClient underneath the transport, outside main.
• server.py — MCPServer(token_verifier=..., auth=AuthSettings(...)) is the whole recipe; streamable_http_app() reads those constructor kwargs and mounts the bearer gate + PRM route.
• server_lowlevel.py — same gate, but lowlevel.Server takes auth= / token_verifier= at streamable_http_app(...) time, not in the constructor. mcp.server.auth.* imports are allowed in lowlevel files (helper-tier).
• whoami() — get_access_token() returns the per-HTTP-request AccessToken. It is not on Context (unlike other SDKs' ctx.authInfo); a later release will namespace it as ctx.transport.auth.

Caveats

• transport_security=NO_DNS_REBIND — DNS-rebinding protection is on by default for localhost binds; the harness disables it because the in-process httpx client sends no Origin header. Drop the kwarg for a real deployment.
• RESOURCE_URL is hard-coded to port 8000 (the harness's in-process origin). If you change --port, edit RESOURCE_URL to match or the PRM document's resource field will be wrong.
• Auth is HTTP-only; over stdio or the in-memory transport get_access_token() returns None and there is no gate.
• The 401/403 status codes and WWW-Authenticate header are HTTP-level and Client cannot observe them; they are pinned by tests/interaction/auth/test_bearer.py and shown via curl above.

Spec

Authorization · RFC 9728 (Protected Resource Metadata) · RFC 6750 (WWW-Authenticate: Bearer)

See also

oauth/ (full authorization-code grant with an in-process AS) · oauth_client_credentials/ (M2M client_credentials grant) · stateless_legacy/ (the un-gated hosting baseline).