diff --git a/backend/app/Http/Middleware/AuthMiddleware.php b/backend/app/Http/Middleware/AuthMiddleware.php
new file mode 100644
index 0000000..8e21ece
--- /dev/null
+++ b/backend/app/Http/Middleware/AuthMiddleware.php
@@ -0,0 +1,51 @@
+<?php
+
+namespace App\Http\Middleware;
+
+use App\Auth\Clock;
+use App\Auth\SessionRepository;
+use Closure;
+use Illuminate\Http\JsonResponse;
+use Illuminate\Http\Request;
+use Symfony\Component\HttpFoundation\Response;
+
+class AuthMiddleware
+{
+    public const COOKIE_NAME = 'auth_token';
+
+    public function __construct(
+        private SessionRepository $sessionRepo,
+        private Clock $clock,
+    ) {}
+
+    /**
+     * @param  Closure(Request): Response  $next
+     */
+    public function handle(Request $request, Closure $next): Response
+    {
+        $token = $request->cookie(self::COOKIE_NAME);
+        if (! is_string($token) || $token === '') {
+            return $this->unauthorized();
+        }
+
+        $session = $this->sessionRepo->findByToken($token);
+        if ($session === null) {
+            return $this->unauthorized();
+        }
+
+        if ($session->isExpired($this->clock->now())) {
+            $this->sessionRepo->deleteByToken($token);
+
+            return $this->unauthorized();
+        }
+
+        $request->attributes->set('user', $session->getUser());
+
+        return $next($request);
+    }
+
+    private function unauthorized(): JsonResponse
+    {
+        return new JsonResponse(['error' => 'unauthenticated'], 401);
+    }
+}