lane-mcp-auth

OAuth 2.1 resource server and consent gate for an MCP server behind Lane — the Python distribution of @lane/mcp-auth.

pip install lane-mcp-auth          # core
pip install 'lane-mcp-auth[fastmcp]'   # + the FastMCP helpers

Your server verifies bearer tokens, publishes the discovery document clients need, and refuses every tool until the caller holds a recorded, revocable grant.

from lane_mcp_auth import LaneMcpAuth

auth = LaneMcpAuth(
    resource="https://acme.example/mcp",
    connections=connections,   # yours: this is server-side state
    exchanger=exchanger,
)

The three tiers

tier	reached by	declared
authenticated only	—	not registrable
any connected caller	completing the step-up	no scope
a specific authority	the step-up granting it	`scope="…"`

Registration is the floor. Omitting a scope means any connected caller, never anyone: a session that has not registered has nothing anyone can revoke, so a tool answering it would be answering something nobody can withdraw.

With FastMCP

from lane_mcp_auth.fastmcp import register_step_up_tool, guarded

register_step_up_tool(mcp, auth)

@mcp.tool()
@guarded(auth, "read_orders", scope="email")
async def read_orders(ctx) -> str:
    return await orders_for(ctx)

Never authorize on the token's scopes

claims.scopes is the token's own claim: empty before the step-up, stale after. Authority lives in the connection and is reachable only through has_scope() / effective_scopes(), because Lane decides it at exchange time and can refuse an exchange it would previously have allowed. A signed claim cannot be withdrawn.

Parity with the TypeScript

Same invariants, same names where Python idiom allows. The TypeScript package is the reference implementation; where the two could drift — scope filtering, the metadata paths, the gate's decision table — see SCOPE.md for what is implemented here and what is not yet.

Licence

MIT

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