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> Discover all available pages from the documentation index: https://mastra.ai/llms.txt

# Middleware

Mastra servers can execute custom middleware functions before or after an API route handler is invoked. This is useful for things like authentication, logging, injecting request-specific context or adding CORS headers.

A middleware receives the [Hono](https://hono.dev) `Context` (`c`) and a `next` function. If it returns a `Response` the request is short-circuited. Calling `next()` continues processing the next middleware or route handler.

> **Note:** Middleware handlers use Hono's signature, so they run on Hono-based serving paths: `mastra dev` and `mastra build`, the [Hono adapter](https://mastra.ai/reference/server/hono-adapter), and adapters built on it such as `@mastra/next` and `@mastra/tanstack-start`. Adapters for other frameworks (Express, Fastify, Koa) can't run Hono handlers and log a warning at startup when middleware is configured. Register middleware through the framework's own API there instead.
>
> User middleware never runs on routes declared public with `requiresAuth: false`, so it can't block endpoints the framework needs to keep reachable, such as the Studio sign-in routes.

```typescript
import { Mastra } from '@mastra/core'

export const mastra = new Mastra({
  server: {
    middleware: [
      {
        handler: async (c, next) => {
          // Example: Add authentication check
          const authHeader = c.req.header('Authorization')
          if (!authHeader) {
            return new Response('Unauthorized', { status: 401 })
          }

          await next()
        },
        path: '/api/*',
      },
      // Add a global request logger
      async (c, next) => {
        console.log(`${c.req.method} ${c.req.url}`)
        await next()
      },
    ],
  },
})
```

To attach middleware to a single route pass the `middleware` option to `registerApiRoute`:

```typescript
registerApiRoute('/my-custom-route', {
  method: 'GET',
  middleware: [
    async (c, next) => {
      console.log(`${c.req.method} ${c.req.url}`)
      await next()
    },
  ],
  handler: async c => {
    const mastra = c.get('mastra')
    return c.json({ message: 'Hello, world!' })
  },
})
```

## Common examples

### Block built-in route groups

Mastra doesn't provide a configuration option to remove or allowlist built-in routes. On Hono-based serving paths, you can make selected route groups unavailable by returning a response without calling `next()`:

```typescript
import { Mastra } from '@mastra/core'

const notFound = async () => new Response('Not Found', { status: 404 })

export const mastra = new Mastra({
  server: {
    middleware: [
      { path: '/api/memory/*', handler: notFound },
      { path: '/api/logs/*', handler: notFound },
      { path: '/api/observability/*', handler: notFound },
    ],
  },
})
```

Each wildcard pattern blocks both the route group itself and its nested routes. For example, `/api/logs/*` blocks `/api/logs` and `/api/logs/transports`. Other route groups remain available.

Generated servers pass `server.apiPrefix` to the Hono adapter's [`prefix` constructor option](https://mastra.ai/reference/server/hono-adapter), which prefixes built-in routes. Middleware paths are registered unchanged, so they must explicitly include the configured prefix. For example, with `apiPrefix: '/api/v2'`, use `/api/v2/memory/*`. Custom API routes must live outside the configured API prefix and aren't blocked by these patterns.

This approach can't block routes declared public with `requiresAuth: false`, because Mastra skips user middleware for those routes. With a non-Hono server adapter, register equivalent middleware through the server framework instead.

### Using `RequestContext`

You can populate `RequestContext` in a runtime server middleware by extracting information from the request. In this example, the `temperature-unit` is set based on the Cloudflare `CF-IPCountry` header to ensure responses match the user's locale.

```typescript
import { Mastra } from '@mastra/core'
import { RequestContext } from '@mastra/core/request-context'
import { testWeatherAgent } from './agents/test-weather-agent'

export const mastra = new Mastra({
  agents: { testWeatherAgent },
  server: {
    middleware: [
      async (context, next) => {
        const country = context.req.header('CF-IPCountry')
        const requestContext = context.get('requestContext')

        requestContext.set('temperature-unit', country === 'US' ? 'fahrenheit' : 'celsius')

        await next()
      },
    ],
  },
})
```

### Authentication

```typescript
{
  handler: async (c, next) => {
    const authHeader = c.req.header('Authorization');
    if (!authHeader || !authHeader.startsWith('Bearer ')) {
      return new Response('Unauthorized', { status: 401 });
    }

    // Validate token here
    await next();
  },
  path: '/api/*',
}
```

### Authorization (User Isolation)

Authentication verifies who the user is, while authorization controls what they can access.

Without server-enforced resource scoping or another authorization policy, authenticated callers can list threads across resources and access their messages and working memory. Callers don't need to guess thread IDs: an unscoped listing can expose them. For private per-user or per-tenant memory, configure `mapUserToResourceId` or set a trusted resource ID in middleware.

Cross-resource access can be intentional in shared applications. A resource ID can identify a user, tenant, project, or another grouping. Choose an authorization policy that matches who can access those resources.

The simplest way to scope memory and threads to the authenticated user is the `mapUserToResourceId` callback in the auth config:

```typescript
import { Mastra } from '@mastra/core'

export const mastra = new Mastra({
  server: {
    auth: {
      authenticateToken: async token => {
        return verifyToken(token) // { id: 'user-123', orgId: 'org-456', ... }
      },
      mapUserToResourceId: user => user.id,
    },
  },
})
```

After successful authentication, `mapUserToResourceId` is called with the authenticated user object. The returned value is set as `MASTRA_RESOURCE_ID_KEY` on the request context, which works across all server adapters (Hono, Express, Next.js, etc.).

When configured, the callback must return a non-empty string. If it throws or returns `null`, `undefined`, an empty or whitespace-only string, or a non-string value, authentication middleware rejects the request with a 500 error before the route runs. This applies to all requests that run authentication, including non-memory routes. A client-provided resource ID can't override a failed mapping.

With `CompositeAuth`, this requirement applies to the provider that authenticated the request. A provider without a mapper keeps its existing behavior, even if another provider in the composite has one. The same validation applies to configured Studio auth mappers.

Without a mapper, authentication doesn't enable user isolation: you're responsible for setting a trusted resource ID in middleware or otherwise enforcing authorization.

The resource ID doesn't have to be `user.id`. Common patterns:

```typescript
// Per-user within an organization
mapUserToResourceId: user => `${user.orgId}:${user.id}`

// From a JWT claim
mapUserToResourceId: user => user.tenantId

// Composite key
mapUserToResourceId: user => `${user.workspaceId}:${user.projectId}:${user.id}`
```

With a resource ID set, the server automatically:

- **Filters thread listing** to only return threads in the configured resource scope
- **Validates thread access** and returns 403 if accessing a thread belonging to a different resource
- **Forces thread creation** to use the configured resource ID
- **Validates message operations** including deletion, ensuring messages belong to threads in the configured resource scope

Even if a client passes `?resourceId=other-resource-id`, the server-set value takes precedence. Attempts to access threads or messages belonging to a different resource return a 403 error. Users mapped to the same resource ID share that resource scope.

#### Advanced: Setting resource ID in middleware

For more complex scenarios (e.g., looking up the resource ID from a database), you can set `MASTRA_RESOURCE_ID_KEY` directly in middleware:

```typescript
import { Mastra } from '@mastra/core'
import { MASTRA_RESOURCE_ID_KEY } from '@mastra/core/request-context'
import { getAuthenticatedUser } from '@mastra/server/auth'

export const mastra = new Mastra({
  server: {
    auth: {
      authenticateToken: async token => verifyToken(token),
    },
    middleware: [
      {
        path: '/api/*',
        handler: async (c, next) => {
          const token = c.req.header('Authorization')
          if (!token) {
            return c.json({ error: 'Unauthorized' }, 401)
          }

          const user = await getAuthenticatedUser<{ id: string }>({
            mastra: c.get('mastra'),
            token,
            request: c.req.raw,
          })
          const requestContext = c.get('requestContext')

          if (!user) {
            return c.json({ error: 'Unauthorized' }, 401)
          }

          requestContext.set(MASTRA_RESOURCE_ID_KEY, user.id)
          return next()
        },
      },
    ],
  },
})
```

`server.middleware` runs before Mastra's per-route auth checks. When middleware needs the authenticated user, call `getAuthenticatedUser()` to resolve it from the configured auth provider without changing the default route auth flow.

#### Using `MASTRA_THREAD_ID_KEY`

You can also set `MASTRA_THREAD_ID_KEY` to override the client-provided thread ID:

```typescript
import { MASTRA_RESOURCE_ID_KEY, MASTRA_THREAD_ID_KEY } from '@mastra/core/request-context'

// Force operations to use a specific thread
requestContext.set(MASTRA_THREAD_ID_KEY, validatedThreadId)
```

This is useful when you want to restrict operations to a specific thread that you've validated through other means.

### CORS support

```typescript
{
  handler: async (c, next) => {
    c.header('Access-Control-Allow-Origin', '*');
    c.header(
      'Access-Control-Allow-Methods',
      'GET, POST, PUT, DELETE, OPTIONS',
    );
    c.header(
      'Access-Control-Allow-Headers',
      'Content-Type, Authorization',
    );

    if (c.req.method === 'OPTIONS') {
      return new Response(null, { status: 204 });
    }

    await next();
  },
}
```

### Request logging

```typescript
{
  handler: async (c, next) => {
    const start = Date.now();
    await next();
    const duration = Date.now() - start;
    console.log(`${c.req.method} ${c.req.url} - ${duration}ms`);
  },
}
```

# Related

- [Request Context](https://mastra.ai/docs/server/request-context)
- [Reserved Keys](https://mastra.ai/docs/server/request-context)