在登录时，当用户通过身份验证时:

At login, when user is authenticated:

Session["IsLoggedIn"] = "Yes";
//OR
Session["LoggedInUserId"] = "User621";

注销时，清除会话:

At the time of logout, clear the session:

Session.Clear();
//OR 
Session["IsLoggedIn"] = null;

如果要检查用户是否登录，只需查看会话值是否存在.如果它为null，则为空.

If you want to check if user is logged in or not, just see if session value exists. If it''s null then not.