Laravel Middleware: Creating Custom Guards

public function handle($request, Closure $next)
{
    if (!$request->user()->isAdmin()) {
        abort(403);
    }
    return $next($request);
}

public function handle($request, Closure $next, $role)
{
    if (!$request->user()->hasRole($role)) {
        abort(403);
    }
    return $next($request);
}

protected $routeMiddleware = [
    'admin' => \App\Http\Middleware\AdminMiddleware::class,
];