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fastmcp.server.auth.auth

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Classes

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AccessToken

AccessToken that includes all JWT claims.

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TokenHandler

TokenHandler that returns MCP-compliant error responses. This handler addresses two SDK issues:
  1. Error code: The SDK returns unauthorized_client for client authentication failures, but RFC 6749 Section 5.2 requires invalid_client with HTTP 401. This distinction matters for client re-registration behavior.
  2. Status code: The SDK returns HTTP 400 for all token errors including invalid_grant (expired/invalid tokens). However, the MCP spec requires: “Invalid or expired tokens MUST receive a HTTP 401 response.”
This handler transforms responses to be compliant with both OAuth 2.1 and MCP specs. Methods:

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handle 

handle(self, request: Any)
Wrap SDK handle() and transform auth error responses.

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AuthProvider

Base class for all FastMCP authentication providers. This class provides a unified interface for all authentication providers, whether they are simple token verifiers or full OAuth authorization servers. All providers must be able to verify tokens and can optionally provide custom authentication routes. Methods:

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verify_token 

verify_token(self, token: str) -> AccessToken | None
Verify a bearer token and return access info if valid. All auth providers must implement token verification. Args:
  • token: The token string to validate
Returns:
  • AccessToken object if valid, None if invalid or expired

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set_mcp_path 

set_mcp_path(self, mcp_path: str | None) -> None
Set the MCP endpoint path and compute resource URL. This method is called by get_routes() to configure the expected resource URL before route creation. Subclasses can override to perform additional initialization that depends on knowing the MCP endpoint path. Args:
  • mcp_path: The path where the MCP endpoint is mounted (e.g., “/mcp”)

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get_routes 

get_routes(self, mcp_path: str | None = None) -> list[Route]
Get all routes for this authentication provider. This includes both well-known discovery routes and operational routes. Each provider is responsible for creating whatever routes it needs:
  • TokenVerifier: typically no routes (default implementation)
  • RemoteAuthProvider: protected resource metadata routes
  • OAuthProvider: full OAuth authorization server routes
  • Custom providers: whatever routes they need
Args:
  • mcp_path: The path where the MCP endpoint is mounted (e.g., “/mcp”) This is used to advertise the resource URL in metadata, but the provider does not create the actual MCP endpoint route.
Returns:
  • List of all routes for this provider (excluding the MCP endpoint itself)

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get_well_known_routes 

get_well_known_routes(self, mcp_path: str | None = None) -> list[Route]
Get well-known discovery routes for this authentication provider. This is a utility method that filters get_routes() to return only well-known discovery routes (those starting with /.well-known/). Well-known routes provide OAuth metadata and discovery endpoints that clients use to discover authentication capabilities. These routes should be mounted at the root level of the application to comply with RFC 8414 and RFC 9728. Common well-known routes:
  • /.well-known/oauth-authorization-server (authorization server metadata)
  • /.well-known/oauth-protected-resource/* (protected resource metadata)
Args:
  • mcp_path: The path where the MCP endpoint is mounted (e.g., “/mcp”) This is used to construct path-scoped well-known URLs.
Returns:
  • List of well-known discovery routes (typically mounted at root level)

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get_middleware 

get_middleware(self) -> list
Get HTTP application-level middleware for this auth provider. Returns:
  • List of Starlette Middleware instances to apply to the HTTP app

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TokenVerifier

Base class for token verifiers (Resource Servers). This class provides token verification capability without OAuth server functionality. Token verifiers typically don’t provide authentication routes by default. Methods:

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verify_token 

verify_token(self, token: str) -> AccessToken | None
Verify a bearer token and return access info if valid.

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RemoteAuthProvider

Authentication provider for resource servers that verify tokens from known authorization servers. This provider composes a TokenVerifier with authorization server metadata to create standardized OAuth 2.0 Protected Resource endpoints (RFC 9728). Perfect for:
  • JWT verification with known issuers
  • Remote token introspection services
  • Any resource server that knows where its tokens come from
Use this when you have token verification logic and want to advertise the authorization servers that issue valid tokens. Methods:

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verify_token 

verify_token(self, token: str) -> AccessToken | None
Verify token using the configured token verifier.

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get_routes 

get_routes(self, mcp_path: str | None = None) -> list[Route]
Get routes for this provider. Creates protected resource metadata routes (RFC 9728).

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OAuthProvider

OAuth Authorization Server provider. This class provides full OAuth server functionality including client registration, authorization flows, token issuance, and token verification. Methods:

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verify_token 

verify_token(self, token: str) -> AccessToken | None
Verify a bearer token and return access info if valid. This method implements the TokenVerifier protocol by delegating to our existing load_access_token method. Args:
  • token: The token string to validate
Returns:
  • AccessToken object if valid, None if invalid or expired

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get_routes 

get_routes(self, mcp_path: str | None = None) -> list[Route]
Get OAuth authorization server routes and optional protected resource routes. This method creates the full set of OAuth routes including:
  • Standard OAuth authorization server routes (/.well-known/oauth-authorization-server, /authorize, /token, etc.)
  • Optional protected resource routes
Returns:
  • List of OAuth routes

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get_well_known_routes 

get_well_known_routes(self, mcp_path: str | None = None) -> list[Route]
Get well-known discovery routes with RFC 8414 path-aware support. Overrides the base implementation to support path-aware authorization server metadata discovery per RFC 8414. If issuer_url has a path component, the authorization server metadata route is adjusted to include that path. For example, if issuer_url is “http://example.com/api”, the discovery endpoint will be at “/.well-known/oauth-authorization-server/api” instead of just “/.well-known/oauth-authorization-server”. Args:
  • mcp_path: The path where the MCP endpoint is mounted (e.g., “/mcp”)
Returns:
  • List of well-known discovery routes