# Authorization

This page covers OAuth 2.1 authentication for both MCP servers and clients.

## Server-Side Authentication

Authentication can be used by servers that want to expose tools accessing protected resources.

`mcp.server.auth` implements OAuth 2.1 resource server functionality, where MCP servers act as Resource Servers (RS) that validate tokens issued by separate Authorization Servers (AS). This follows the [MCP authorization specification](https://modelcontextprotocol.io/specification/2025-11-25/basic/authorization) and implements RFC 9728 (Protected Resource Metadata) for AS discovery.

MCP servers can use authentication by providing an implementation of the `TokenVerifier` protocol:

<!-- snippet-source examples/snippets/servers/oauth_server.py -->
```python
"""
Run from the repository root:
    uv run examples/snippets/servers/oauth_server.py
"""

from pydantic import AnyHttpUrl

from mcp.server.auth.provider import AccessToken, TokenVerifier
from mcp.server.auth.settings import AuthSettings
from mcp.server.fastmcp import FastMCP


class SimpleTokenVerifier(TokenVerifier):
    """Simple token verifier for demonstration."""

    async def verify_token(self, token: str) -> AccessToken | None:
        pass  # This is where you would implement actual token validation


# Create FastMCP instance as a Resource Server
mcp = FastMCP(
    "Weather Service",
    json_response=True,
    # Token verifier for authentication
    token_verifier=SimpleTokenVerifier(),
    # Auth settings for RFC 9728 Protected Resource Metadata
    auth=AuthSettings(
        issuer_url=AnyHttpUrl("https://auth.example.com"),  # Authorization Server URL
        resource_server_url=AnyHttpUrl("http://localhost:3001"),  # This server's URL
        required_scopes=["user"],
    ),
)


@mcp.tool()
async def get_weather(city: str = "London") -> dict[str, str]:
    """Get weather data for a city"""
    return {
        "city": city,
        "temperature": "22",
        "condition": "Partly cloudy",
        "humidity": "65%",
    }


if __name__ == "__main__":
    mcp.run(transport="streamable-http")
```

_Full example: [examples/snippets/servers/oauth_server.py](https://github.com/modelcontextprotocol/python-sdk/blob/v1.x/examples/snippets/servers/oauth_server.py)_
<!-- /snippet-source -->

For a complete example with separate Authorization Server and Resource Server implementations, see [`examples/servers/simple-auth/`](https://github.com/modelcontextprotocol/python-sdk/tree/v1.x/examples/servers/simple-auth).

**Architecture:**

- **Authorization Server (AS)**: Handles OAuth flows, user authentication, and token issuance
- **Resource Server (RS)**: Your MCP server that validates tokens and serves protected resources
- **Client**: Discovers AS through RFC 9728, obtains tokens, and uses them with the MCP server

See [TokenVerifier](https://github.com/modelcontextprotocol/python-sdk/blob/v1.x/src/mcp/server/auth/provider.py) for more details on implementing token validation.

## Client-Side Authentication

The SDK includes [authorization support](https://modelcontextprotocol.io/specification/2025-11-25/basic/authorization) for connecting to protected MCP servers:

<!-- snippet-source examples/snippets/clients/oauth_client.py -->
```python
"""
Before running, specify running MCP RS server URL.
To spin up RS server locally, see
    examples/servers/simple-auth/README.md

cd to the `examples/snippets` directory and run:
    uv run oauth-client
"""

import asyncio
from urllib.parse import parse_qs, urlparse

import httpx
from pydantic import AnyUrl

from mcp import ClientSession
from mcp.client.auth import OAuthClientProvider, TokenStorage
from mcp.client.streamable_http import streamable_http_client
from mcp.shared.auth import OAuthClientInformationFull, OAuthClientMetadata, OAuthToken


class InMemoryTokenStorage(TokenStorage):
    """Demo In-memory token storage implementation."""

    def __init__(self):
        self.tokens: OAuthToken | None = None
        self.client_info: OAuthClientInformationFull | None = None

    async def get_tokens(self) -> OAuthToken | None:
        """Get stored tokens."""
        return self.tokens

    async def set_tokens(self, tokens: OAuthToken) -> None:
        """Store tokens."""
        self.tokens = tokens

    async def get_client_info(self) -> OAuthClientInformationFull | None:
        """Get stored client information."""
        return self.client_info

    async def set_client_info(self, client_info: OAuthClientInformationFull) -> None:
        """Store client information."""
        self.client_info = client_info


async def handle_redirect(auth_url: str) -> None:
    print(f"Visit: {auth_url}")


async def handle_callback() -> tuple[str, str | None]:
    callback_url = input("Paste callback URL: ")
    params = parse_qs(urlparse(callback_url).query)
    return params["code"][0], params.get("state", [None])[0]


async def main():
    """Run the OAuth client example."""
    oauth_auth = OAuthClientProvider(
        server_url="http://localhost:8001",
        client_metadata=OAuthClientMetadata(
            client_name="Example MCP Client",
            redirect_uris=[AnyUrl("http://localhost:3000/callback")],
            grant_types=["authorization_code", "refresh_token"],
            response_types=["code"],
            scope="user",
        ),
        storage=InMemoryTokenStorage(),
        redirect_handler=handle_redirect,
        callback_handler=handle_callback,
    )

    async with httpx.AsyncClient(auth=oauth_auth, follow_redirects=True) as custom_client:
        async with streamable_http_client("http://localhost:8001/mcp", http_client=custom_client) as (read, write, _):
            async with ClientSession(read, write) as session:
                await session.initialize()

                tools = await session.list_tools()
                print(f"Available tools: {[tool.name for tool in tools.tools]}")

                resources = await session.list_resources()
                print(f"Available resources: {[r.uri for r in resources.resources]}")


def run():
    asyncio.run(main())


if __name__ == "__main__":
    run()
```

_Full example: [examples/snippets/clients/oauth_client.py](https://github.com/modelcontextprotocol/python-sdk/blob/v1.x/examples/snippets/clients/oauth_client.py)_
<!-- /snippet-source -->

For a complete working example, see [`examples/clients/simple-auth-client/`](https://github.com/modelcontextprotocol/python-sdk/tree/v1.x/examples/clients/simple-auth-client).
