AuthKit 🤝 FastMCP - Fastmcp

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This guide shows you how to secure your FastMCP server using WorkOS's AuthKit, a complete authentication and user management solution. This integration uses the Remote OAuth pattern, where AuthKit handles user login and your FastMCP server validates the tokens.

Configuration

Prerequisites

Before you begin, you will need:

A WorkOS Account and a new Project.
An AuthKit instance configured within your WorkOS project.
Your FastMCP server's URL (can be localhost for development, e.g., http://localhost:8000).

Step 1: AuthKit Configuration

In your WorkOS Dashboard, enable AuthKit and configure the following settings:

<Steps> <Step title="Enable Dynamic Client Registration"> Go to **Applications → Configuration** and enable **Dynamic Client Registration**. This allows MCP clients register with your application automatically.

![Enable Dynamic Client Registration](./images/authkit/enable_dcr.png)

</Step> <Step title="Note Your AuthKit Domain"> Find your **AuthKit Domain** on the configuration page. It will look like `https://your-project-12345.authkit.app`. You'll need this for your FastMCP server configuration. </Step> </Steps>

Step 2: FastMCP Configuration

Create your FastMCP server file and use the AuthKitProvider to handle all the OAuth integration automatically:

python

from fastmcp import FastMCP
from fastmcp.server.auth.providers.workos import AuthKitProvider

# The AuthKitProvider automatically discovers WorkOS endpoints
# and configures JWT token validation
auth_provider = AuthKitProvider(
    authkit_domain="https://your-project-12345.authkit.app",
    base_url="http://localhost:8000"  # Use your actual server URL
)

mcp = FastMCP(name="AuthKit Secured App", auth=auth_provider)

Testing

To test your server, you can use the fastmcp CLI to run it locally. Assuming you've saved the above code to server.py (after replacing the authkit_domain and base_url with your actual values!), you can run the following command:

bash

fastmcp run server.py --transport http --port 8000

Now, you can use a FastMCP client to test that you can reach your server after authenticating:

python

from fastmcp import Client
import asyncio

async def main():
    async with Client("http://localhost:8000/mcp", auth="oauth") as client:
        assert await client.ping()

if __name__ == "__main__":
    asyncio.run(main())

Environment Variables

For production deployments, use environment variables instead of hardcoding credentials.

Provider Selection

Setting this environment variable allows the AuthKit provider to be used automatically without explicitly instantiating it in code.

<Card> <ParamField path="FASTMCP_SERVER_AUTH" default="Not set"> Set to `fastmcp.server.auth.providers.workos.AuthKitProvider` to use AuthKit authentication. </ParamField> </Card>

AuthKit-Specific Configuration

These environment variables provide default values for the AuthKit provider, whether it's instantiated manually or configured via FASTMCP_SERVER_AUTH.

<Card> <ParamField path="FASTMCP_SERVER_AUTH_AUTHKITPROVIDER_AUTHKIT_DOMAIN" required> Your AuthKit domain (e.g., `https://your-project-12345.authkit.app`) </ParamField> <ParamField path="FASTMCP_SERVER_AUTH_AUTHKITPROVIDER_BASE_URL" required> Public URL of your FastMCP server (e.g., `https://your-server.com` or `http://localhost:8000` for development) </ParamField> <ParamField path="FASTMCP_SERVER_AUTH_AUTHKITPROVIDER_REQUIRED_SCOPES" default="[]"> Comma-, space-, or JSON-separated list of required OAuth scopes (e.g., `openid profile email` or `["openid", "profile", "email"]`) </ParamField> </Card>

Example .env file:

bash

# Use the AuthKit provider
FASTMCP_SERVER_AUTH=fastmcp.server.auth.providers.workos.AuthKitProvider

# AuthKit configuration
FASTMCP_SERVER_AUTH_AUTHKITPROVIDER_AUTHKIT_DOMAIN=https://your-project-12345.authkit.app
FASTMCP_SERVER_AUTH_AUTHKITPROVIDER_BASE_URL=https://your-server.com
FASTMCP_SERVER_AUTH_AUTHKITPROVIDER_REQUIRED_SCOPES=openid,profile,email

With environment variables set, your server code simplifies to:

python

from fastmcp import FastMCP

# Authentication is automatically configured from environment
mcp = FastMCP(name="AuthKit Secured App")