Redirect to previous url Or back() after login/register in Laravel 5.3

I am using laravel 5.3. Suppose I am at (url.com)/posts/5 in a laravel application. Now I want to login. After login I want to redirect back to this url. All I want to edit only these lines in Auth Controller. protected $redirectTo = '/'; as Here says in comment Where to redirect users after login / registration.

class LoginController extends Controller
{
  use AuthenticatesUsers;

  /**
   * Where to redirect users after login / registration.
   *
   * @var string
   */
  protected $redirectTo = '/';


  public function __construct()
  {
      $this->middleware('guest', ['except' => 'logout']);
  }
} 

How can I do that? Note: I am using laravel built-in authentication.

via Chebli Mohamed