# Source: https://gofastmcp.com/python-sdk/fastmcp-server-auth-auth.md

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# auth

# `fastmcp.server.auth.auth`

## Classes

### `AccessToken` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/server/auth/auth.py#L43" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

AccessToken that includes all JWT claims.

### `TokenHandler` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/server/auth/auth.py#L49" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

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:**

#### `handle` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/server/auth/auth.py#L65" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python  theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
handle(self, request: Any)
```

Wrap SDK handle() and transform auth error responses.

### `AuthProvider` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/server/auth/auth.py#L111" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

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:**

#### `verify_token` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/server/auth/auth.py#L140" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python  theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
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

#### `set_mcp_path` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/server/auth/auth.py#L153" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python  theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
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")

#### `get_routes` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/server/auth/auth.py#L167" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python  theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
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)

#### `get_well_known_routes` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/server/auth/auth.py#L190" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python  theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
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)

#### `get_middleware` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/server/auth/auth.py#L222" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python  theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
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

### `TokenVerifier` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/server/auth/auth.py#L256" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

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:**

#### `verify_token` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/server/auth/auth.py#L277" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python  theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
verify_token(self, token: str) -> AccessToken | None
```

Verify a bearer token and return access info if valid.

### `RemoteAuthProvider` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/server/auth/auth.py#L282" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

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:**

#### `verify_token` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/server/auth/auth.py#L323" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python  theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
verify_token(self, token: str) -> AccessToken | None
```

Verify token using the configured token verifier.

#### `get_routes` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/server/auth/auth.py#L327" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python  theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
get_routes(self, mcp_path: str | None = None) -> list[Route]
```

Get routes for this provider.

Creates protected resource metadata routes (RFC 9728).

### `OAuthProvider` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/server/auth/auth.py#L355" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

OAuth Authorization Server provider.

This class provides full OAuth server functionality including client registration,
authorization flows, token issuance, and token verification.

**Methods:**

#### `verify_token` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/server/auth/auth.py#L418" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python  theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
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

#### `get_routes` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/server/auth/auth.py#L433" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python  theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
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

#### `get_well_known_routes` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/server/auth/auth.py#L512" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python  theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
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](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