OAuth 2.1 MCP Server as a Next.js app on Vercel

This is a Next.js-based application that provides an MCP (Model Context Protocol) server with OAuth 2.1 authentication support. It is intended as a model for building your own MCP server in a Next.js context. It uses the @vercel/mcp-adapter to handle the MCP protocol, in order to support both SSE and Streamable HTTP transports.

In addition to being an OAuth server, it also requires the user authenticate. This is currently configured to use Google as a provider, but you could authenticate users however you want (X, GitHub, your own user/password database etc.) without breaking the OAuth flow.

Using with

Claude Desktop and Claude.ai

Claude currently supports only the older SSE transport, so you need to give it a different URL to all the other clients listed here.

Use the "Connect Apps" button and select "Add Integration". Provide the URL like https://example.com/mcp/sse (the /sse at the end is important!). Note that Claude Desktop and Web will not accept a localhost URL.

Cursor

Edit your mcp.json to look like this:

{
  "mcpServers": {
      "MyServer": {
        "name": "LlamaIndex MCP Demo",
        "url": "https://example.com/mcp/mcp",
        "transport": "http-stream"
      },
  }
}

VSCode

VSCode currently doesn't properly evict the client ID, so client registration fails if you accidentally delete the client (the workaround in that issue will resolve it). Otherwise, it works fine. Add this to your settings.json:

"mcp": {
    "servers": {
        "My Server": {
            "url": "https://example.com/mcp/mcp"
        }
    }
}

MCP Inspector

Tell Inspector to connect to https://example.com/mcp/mcp, with Streamable HTTP transport. You can also use the SSE transport by connecting to https://example.com/mcp/sse instead.

Running the server

npm install
prisma generate
npm run dev

The very first time you will also need to run prisma db push to create the database tables.

Environment variables

Required environment variables should be in .env: (not .env.local because Prisma doesn't support it)

DATABASE_URL="postgresql://user:pass@server/database"
AUTH_SECRET="any random string"
GOOGLE_CLIENT_ID="a Google OAuth client ID"
GOOGLE_CLIENT_SECRET="a Google OAuth client secret"
REDIS_URL="rediss://user:pass@host:6379"

DATABASE_URL is required for OAuth authentication to work, this is where sessions etc. live.

REDIS_URL is required if you need SSE transport to work (i.e. you want to support Claude Desktop and Web).

Architecture

If you're using this as a template for your own Next.js app, the important parts are:

• /src/app/api/oauth/* - these implement oauth client registration and token exchange
• /src/app/oauth/authorize/page.tsx - this implements the oauth consent screen (it's extremely basic right now)
• /src/mcp/[transport]/route.ts - this implements the MCP server itself. Your tools, resources, etc. should be defined here.

To handle OAuth your app needs to be able to persist clients, access tokens, etc.. To do this it's using a PostgreSQL database accessed via Prisma. You can swap this for some other database if you want (it will be easiest if it's another Prisma-supported database).

You'll also notice:

• src/app/auth.ts - this implements Auth.js authentication to your app itself. It's configured to use Google as a provider, but you can change it to use any other provider supports by Auth.js. This is not required for the MCP server to work, but it's a good idea to have it in place for your own app.
• src/app/api/auth/[...nextauth]/route.ts - this plumbs in the Auth.js authentication, and is again not part of the OAuth implementation.

Deploying to production

This app only works if deployed to Vercel currently, due to its dependence on the @vercel/mcp-adapter package, which in turn is required to support the old SSE transport. We didn't feel like implementing a whole extra protocol just for Claude Desktop.

Deploy as usual. You'll need to add prisma generate to your build command, and of course you'll need all the same environment variables as in the development environment.