feat: implement admin authentication

app/Http/Middleware/AdminAuth.php

@@ -0,0 +1,20 @@
+<?php
+
+namespace App\Http\Middleware;
+
+use Closure;
+use Illuminate\Http\Request;
+use Illuminate\Support\Facades\Auth;
+use Symfony\Component\HttpFoundation\Response;
+
+class AdminAuth
+{
+    public function handle(Request $request, Closure $next): Response
+    {
+        if (!Auth::guard('admin')->check()) {
+            return redirect()->route('admin.login');
+        }
+
+        return $next($request);
+    }
+}