在5.3中，中间件尚未在constructor中运行，因此您无法收集session数据.但是，使用基于闭包的方法，您应该可以通过以下方式访问它:

In 5.3 the middleware hasn't run yet in the constructor, so you're unable to gather session data. But using your closure-based approach, you should be able to access it with something like this:

$this->middleware(function($request, $next) {
    // Get the session value (uses global helper)
    $this->token = session('_admin_id');

    // If the value is null, abort the request
    if (null === $this->token) abort(404);

    return $next($request);
});