UNIT3D-Community-Edition/app/Http/Middleware/CheckForAdmin.php

<?php

namespace App\Http\Middleware;

use Closure;
use Illuminate\Support\Facades\Auth;
use Symfony\Component\HttpKernel\Exception\NotFoundHttpException;

class CheckForAdmin
{
    /**
     * Handle an incoming request.
     *
     * @param  \Illuminate\Http\Request $request
     * @param  \Closure $next
     * @return mixed
     */
    public function handle($request, Closure $next)
    {
        if (!Auth::check() || !Auth::user()->group->is_admin) {
            throw new NotFoundHttpException;
        }

        return $next($request);
    }
}