C＃，User.GetUser（）为null时授权用户

Question

如何做到这一点，用户在Membership.GetUser() == null？

时进行了身份验证

[Authorize]
public class UserController : Controller
{    
     public ActionResult DoSomething()
     {
        var user =  Membership.GetUser();    // user can access here and be null

     }
}

Link to Web.confing