Clerk MCP Server Template

Clerk MCP Server Template

A production-ready template for building Model Context Protocol (MCP) servers with Clerk authentication on Cloudflare Workers. This template provides everything you need to create secure, authenticated MCP tools that integrate with your existing Clerk-powered applications.

Features

• ✅ Clerk Authentication Integration - Complete OAuth 2.0 flow with Clerk
• ✅ Cloudflare Workers - Serverless edge computing with global distribution
• ✅ Durable Objects - Persistent MCP session state management
• ✅ KV Storage - Temporary OAuth session storage
• ✅ Security - HMAC-signed state parameters and automatic token refresh
• ✅ TypeScript - Full type safety throughout the codebase
• ✅ Example Tools - Ready-to-use example MCP tools
• ✅ Development Tools - ESLint, Prettier, and MCP Inspector integration

Why This Template?

This template bridges your existing Clerk-authenticated application with Claude AI through MCP tools. Perfect for:

• SaaS Applications: Give Claude access to your user data and business logic
• Customer Support: Let Claude query your systems with proper user context
• Data Analysis: Provide Claude with authenticated access to your APIs
• Workflow Automation: Create secure, user-specific automations

Quick Start

1. Prerequisites

• Node.js 22.x or later
• A Clerk account with API keys
• A Cloudflare account with Workers enabled
• An existing application using Clerk for authentication

2. Use This Template

git clone https://github.com/your-username/clerk-mcp-template.git my-mcp-server
cd my-mcp-server
npm install

3. Configure Environment Variables

Copy the example environment file:

cp .dev.vars.example .dev.vars

Update .dev.vars with your Clerk keys and app URL:

CLERK_SECRET_KEY=sk_test_your_actual_clerk_secret_key
CLERK_PUBLISHABLE_KEY=pk_test_your_actual_clerk_publishable_key
APP_URL=https://your-app.com

Important: APP_URL should point to your existing Clerk-authenticated application where you'll implement the MCP auth flow.

4. Create KV Namespace

Create a KV namespace for OAuth session storage:

wrangler kv:namespace create "OAUTH_KV"

Update the id in wrangler.jsonc with the generated namespace ID.

5. Update Configuration

wrangler.jsonc:

• Change name from "your-mcp-server" to your desired worker name
• Update the KV namespace ID with the one generated above

src/index.ts:

• Update the server name and version in the McpServer constructor
• Replace example tools with your own (see examples below)

6. Start Development

npm run dev

The server will be available at http://localhost:8788

Architecture

graph TB
    A[MCP Client] --> B[Cloudflare Worker]
    B --> C[OAuth Provider]
    C --> D[Clerk Authentication]
    B --> E[Durable Objects]
    B --> F[KV Storage]
    B --> G[Your API]

    E --> H[MCP Session State]
    F --> I[OAuth Sessions]
    D --> J[User Authentication]
    G --> K[Your Application Data]

Authentication Flow

1. MCP Client connects to /sse endpoint
2. OAuth redirect to /authorize endpoint
3. User authentication via Clerk (you implement this part)
4. Token exchange at /callback endpoint
5. Session creation in Durable Objects
6. MCP tools become available with authenticated context

Integrating with Your Application

Step 1: Add MCP Authentication Route

Create an authentication route in your existing Clerk application at /auth/mcp. This route handles the OAuth flow initiated by the MCP server.

React Router v7 (Framework Mode) Example

This example shows integration with React Router v7 in framework mode (formerly Remix), but you can adapt it to Next.js, Express, or any framework.

app/routes/auth.mcp.tsx:

import { createClerkClient } from '@clerk/express'
import { redirect, type LoaderFunctionArgs } from 'react-router'

export async function loader({ request }: LoaderFunctionArgs) {
	const url = new URL(request.url)
	const state = url.searchParams.get('state')
	const callbackUrl = url.searchParams.get('callback_url')
	const clientName = url.searchParams.get('client_name')

	if (!state || !callbackUrl) {
		throw new Error('Missing required parameters')
	}

	// Get the authenticated user's session token
	const clerkClient = createClerkClient({
		secretKey: process.env.CLERK_SECRET_KEY,
		publishableKey: process.env.CLERK_PUBLISHABLE_KEY,
	})

	const clerkAuth = (await clerkClient.authenticateRequest(request)).toAuth()
	const sessionToken = await clerkAuth?.getToken()

	if (!sessionToken) {
		// Redirect to sign-in if not authenticated
		const signInUrl = new URL('/sign-in', request.url)
		signInUrl.searchParams.set('redirect_url', request.url)
		return redirect(signInUrl.toString())
	}

	// Redirect back to MCP server with token
	const redirectUrl = new URL(callbackUrl)
	redirectUrl.searchParams.set('clerk_token', sessionToken)
	redirectUrl.searchParams.set('state', state)

	return redirect(redirectUrl.toString())
}

// Optional: Add a component for showing consent screen
export default function McpAuth() {
	return (
		<div className="max-w-md mx-auto mt-8 p-6 bg-white rounded-lg shadow-md">
			<h1 className="text-xl font-bold mb-4">Authorize MCP Access</h1>
			<p className="text-gray-600 mb-4">
				Claude AI is requesting access to your account data.
			</p>
			<p className="text-sm text-gray-500">
				This will redirect you automatically...
			</p>
		</div>
	)
}

Step 2: Create API Endpoints

Add protected API endpoints in your application that the MCP server can call with authenticated requests.

app/routes/api.users.tsx:

import { createClerkClient } from '@clerk/express'
import { json, type LoaderFunctionArgs } from 'react-router'

export async function loader({ request }: LoaderFunctionArgs) {
	try {
		const clerkClient = createClerkClient({
			secretKey: process.env.CLERK_SECRET_KEY,
			publishableKey: process.env.CLERK_PUBLISHABLE_KEY,
		})

		// Verify the request is authenticated
		const clerkAuth = await clerkClient.authenticateRequest(request)
		const userId = clerkAuth.toAuth()?.userId

		if (!userId) {
			return json({ error: 'Unauthorized' }, { status: 401 })
		}

		// Your business logic here
		const users = await getUsersForCurrentUser(userId)

		return { users }
	} catch (error) {
		return json({ error: 'Internal server error' }, { status: 500 })
	}
}

Step 3: Customize MCP Tools

Replace the example tools in src/index.ts with your own:

// Custom tool example
this.server.tool(
	'getUsers',
	'Fetch all users from your application',
	{},
	this.requireAuth(async () => {
		const users = await this.makeApiRequest('api/users')

		return {
			content: [
				{
					type: 'text',
					text: `Found ${users.length} users:\n${JSON.stringify(users, null, 2)}`,
				},
			],
		}
	}),
)

Configuration Reference

Environment Variables

Variable	Description	Required
CLERK_SECRET_KEY	Your Clerk secret key	✅
CLERK_PUBLISHABLE_KEY	Your Clerk publishable key	✅
APP_URL	Your application URL	✅

Add your own application-specific environment variables to the Env interface in src/types.ts.

Clerk JWT Templates

Create a JWT template in your Clerk Dashboard for token generation:

1. Go to JWT Templates in your Clerk Dashboard
2. Create a new template (e.g., "mcp-server")
3. Update the template name in src/index.ts:

const token = await getToken(
	// ... token manager
	(this as any).env.CLERK_SECRET_KEY,
	'your-template-name', // Update this
)

Development

Available Scripts

npm run dev        # Start development server
npm run deploy     # Deploy to Cloudflare Workers
npm run inspect    # Launch MCP Inspector
npm run lint       # Run ESLint + format
npm run typecheck  # Run TypeScript type checking
npm run validate   # Run typecheck + lint

Testing with MCP Inspector

1. Start the development server: npm run dev
2. Open MCP Inspector
3. Set transport type to SSE
4. Connect to http://localhost:8788/sse
5. Complete the authentication flow
6. Test your tools

Deployment

1. Set Production Secrets

wrangler secret put CLERK_SECRET_KEY
wrangler secret put CLERK_PUBLISHABLE_KEY
wrangler secret put APP_URL

2. Create Production KV Namespace

wrangler kv:namespace create "OAUTH_KV" --env production

Update the production KV namespace ID in wrangler.jsonc.

3. Deploy and Configure

npm run deploy

Add your deployed server to Claude Desktop MCP configuration:

{
	"mcpServers": {
		"my-app": {
			"command": "npx",
			"args": [
				"@modelcontextprotocol/server-remote",
				"https://your-mcp-server.your-subdomain.workers.dev/sse"
			]
		}
	}
}

Project Structure

clerk-mcp-template/
├── src/
│   ├── index.ts      # Main MCP server class and tools
│   ├── auth.ts       # OAuth authentication handlers
│   ├── clerk.ts      # Clerk authentication utilities
│   ├── utils.ts      # Utility functions (HMAC, logging, etc.)
│   └── types.ts      # TypeScript type definitions
├── wrangler.jsonc    # Cloudflare Worker configuration
├── package.json      # Dependencies and scripts
├── tsconfig.json     # TypeScript configuration
├── eslint.config.js  # ESLint configuration
├── .dev.vars         # Development environment variables
└── README.md         # This file

Security Considerations

• OAuth 2.0 ensures secure authentication flow
• HMAC signatures protect state parameters from tampering
• Automatic token refresh handles session expiration
• Session cleanup removes expired OAuth sessions
• Secure headers include proper CORS and authentication headers

Troubleshooting

Common Issues

Authentication fails:

• Verify Clerk API keys are correct
• Ensure your authentication route is implemented
• Check that JWT template exists in Clerk Dashboard

KV namespace errors:

• Verify namespace ID in wrangler.jsonc
• Ensure namespace is created and bound

Tools not working:

• Check that user is authenticated
• Verify API endpoints are correct
• Review Cloudflare Workers logs

Debugging

# View real-time logs
wrangler tail

# Check deployment status
wrangler deployments list

# Test locally with debugging
npm run dev

Contributing

1. Fork this repository
2. Create a feature branch: git checkout -b feature/amazing-feature
3. Commit your changes: git commit -m 'Add amazing feature'
4. Push to the branch: git push origin feature/amazing-feature
5. Open a Pull Request

Resources

• Model Context Protocol Specification
• Clerk Authentication Documentation
• Cloudflare Workers Documentation
• Cloudflare MCP Examples
• React Router v7 Documentation

License

MIT License - see LICENSE file for details.