Only allow a single user to register

app/Http/Middleware/AllowOnlyOneUser.php

@@ -0,0 +1,26 @@
+<?php
+
+namespace App\Http\Middleware;
+
+use App\Models\User;
+
+use Closure;
+use Illuminate\Http\Request;
+use Symfony\Component\HttpFoundation\Response;
+
+class AllowOnlyOneUser
+{
+    /**
+     * Handle an incoming request.
+     *
+     * @param  \Closure(\Illuminate\Http\Request): (\Symfony\Component\HttpFoundation\Response)  $next
+     */
+    public function handle(Request $request, Closure $next): Response
+    {
+        if (User::exists()) {
+            abort(403, 'Registration is closed.');
+        }
+
+        return $next($request);
+    }
+}

routes/auth.php

@@ -1,6 +1,7 @@
 <?php
 
 use App\Http\Controllers\Auth\VerifyEmailController;
+use App\Http\Middleware\AllowOnlyOneUser;
 use App\Livewire\Auth\ConfirmPassword;
 use App\Livewire\Auth\ForgotPassword;
 use App\Livewire\Auth\Login;
@@ -11,7 +12,7 @@ use Illuminate\Support\Facades\Route;
 
 Route::middleware('guest')->group(function () {
     Route::get('login', Login::class)->name('login');
-    Route::get('register', Register::class)->name('register');
+    Route::get('register', Register::class)->name('register')->middleware(AllowOnlyOneUser::class);
     Route::get('forgot-password', ForgotPassword::class)->name('password.request');
     Route::get('reset-password/{token}', ResetPassword::class)->name('password.reset');
 });