web中間件從5.2.27版本以后默認全局加載，不需要自己手動載入，如果自己手動重復載入，會導致session無法加載等情況。
下面是Laravel默認為我們提供的web和api中間件組的代碼：

protected $middlewareGroups = [
    'web' => [
        \App\Http\Middleware\EncryptCookies::class,
        \Illuminate\Cookie\Middleware\AddQueuedCookiesToResponse::class,
        \Illuminate\Session\Middleware\StartSession::class,
        \Illuminate\View\Middleware\ShareErrorsFromSession::class,
        \App\Http\Middleware\VerifyCsrfToken::class,
    ],

    'api' => [
        'throttle:60,1',
    ],
];