MCP Request Auth End-to-End Flow

This diagram shows the end-to-end authentication lifecycle of an MCP request. It traces the request from a client, through the gateway, to a downstream MCP server.

Core Concepts for Beginners

• Reverse Proxy: A server that authenticates users and passes identity headers to the gateway.
• Bearer Token: A secret key sent in the Authorization: Bearer <token> header.
• AuthShape: The credential format required by a downstream server (Bearer token, Basic auth, custom header, or query parameter).

Auth & Setup Matrix Reference

This flow combines three security layers:

1. Client Identity: The gateway resolves caller identity from SSO headers or AppKey records.
2. Server Auth Requirement: The downstream server specifies its credential format (AuthShape).
3. Secret Origin: The gateway retrieves a shared secret (Vault, Env) or a personal secret (UserProvided). It formats the credential and forwards the request transparently.

WARNING

Dynamic Token Limitation: The gateway does not mint dynamic tokens (such as short-lived JWTs) on behalf of users. Configured secret providers return static credentials.

If a backend server requires a dynamic JWT, the client must obtain the token first. The client sends the token in the X-Target-Auth header. When the server has AllowPassThroughAuth: true, the gateway formats this token into the target AuthShape before forwarding the request.