# API Key (/docs/authentication/api-key)

To enable API key authentication, you can use the `apiKeyAuthMiddleware` middleware on your app.

```typescript title="src/middleware.ts"
import { apiKeyAuthMiddleware, type Middleware } from "xmcp";

const middleware: Middleware = [
  apiKeyAuthMiddleware({
    headerName: "x-api-key",
    apiKey: "12345",
  }),
  // ... other middlewares
];

export default middleware;
```

If no `headerName` is provided, the middleware will default to `x-api-key`.

This middleware can also be used with a validation function. It should **return a boolean** value indicating if the API key is valid.

```typescript title="src/middleware.ts"
import { apiKeyAuthMiddleware, type Middleware } from "xmcp";

const middleware: Middleware = apiKeyAuthMiddleware({
  headerName: "x-api-key",
  validateApiKey: async (apiKey) => {
    return apiKey === "12345";
  },
});

export default middleware;
```

Next time you connect to your MCP server, you'll need to provide the API key in the `x-api-key` header (or the name you specified in the middleware).

Your connection object will look like this:

```json
{
  "mcpServers": {
    "my-project": {
      "url": "http://localhost:3001/mcp",
      "headers": {
        "x-api-key": "12345" // <- This is the API key you provided in the middleware
      }
    }
  }
}
```

Make sure to check the [connecting](/docs/getting-started/connecting) documentation for more details on the different clients.