prefecthq--fastmcp/docs/integrations/authkit.mdx

---
title: AuthKit 🤝 FastMCP
sidebarTitle: AuthKit
description: Secure your FastMCP server with AuthKit by WorkOS
icon: shield-check
---

import { VersionBadge } from "/snippets/version-badge.mdx"

<VersionBadge version="2.11.0" />

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**](/servers/auth/remote-oauth) pattern with [RFC 8707](https://www.rfc-editor.org/rfc/rfc8707.html) resource indicators: AuthKit issues tokens whose `aud` claim is bound to your server's resource URL, and FastMCP validates that claim automatically.

## Configuration

### Prerequisites

Before you begin, you will need:
1.  A **[WorkOS Account](https://workos.com/)** and a new **Project**.
2.  An **[AuthKit](https://www.authkit.com/)** instance configured within your WorkOS project.
3.  Your FastMCP server's URL (can be localhost for development, e.g., `http://127.0.0.1:8000`).

### Step 1: WorkOS Dashboard

In the WorkOS Dashboard, go to **Connect → Configuration** and configure:

<Steps>
<Step title="MCP Auth">
    Enable **Dynamic Client Registration** (DCR) so MCP clients can register themselves. Alternatively, enable **Client ID Metadata Document** (CIMD) if your clients support it.
</Step>

<Step title="MCP resource indicators">
    Add your FastMCP server's resource URL (e.g., `http://127.0.0.1:8000/mcp`) as a valid resource indicator.

    This must exactly match what FastMCP advertises in its protected resource metadata. Start your server first and it will log the correct URL on startup — copy that value.

    Without this step, AuthKit falls back to a default environment-scoped audience and audience validation will fail with a 401.
</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 server.py
from fastmcp import FastMCP
from fastmcp.server.auth.providers.workos import AuthKitProvider

# AuthKitProvider automatically discovers WorkOS endpoints, configures JWT
# validation, and binds the token audience to this server's resource URL.
auth_provider = AuthKitProvider(
    authkit_domain="https://your-project-12345.authkit.app",
    base_url="http://127.0.0.1:8000",  # Use your actual server URL
)

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

When the server starts, it logs the resource URL it is validating against. Paste that URL into your Dashboard's **MCP resource indicators** list.

## 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
```

AuthKit defaults DCR clients to `client_secret_basic` for token exchange, which conflicts with how some MCP clients send credentials. To avoid token exchange errors, register as a public client by setting `token_endpoint_auth_method` to `"none"`:

```python client.py
from fastmcp import Client
from fastmcp.client.auth import OAuth
import asyncio

auth = OAuth(additional_client_metadata={"token_endpoint_auth_method": "none"})

async def main():
    async with Client("http://127.0.0.1:8000/mcp", auth=auth) as client:
        assert await client.ping()

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

## Production Configuration

For production deployments, load sensitive configuration from environment variables:

```python server.py
import os
from fastmcp import FastMCP
from fastmcp.server.auth.providers.workos import AuthKitProvider

# Load configuration from environment variables
auth = AuthKitProvider(
    authkit_domain=os.environ.get("AUTHKIT_DOMAIN"),
    base_url=os.environ.get("BASE_URL", "https://your-server.com"),
)

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