我个人来看实现成员身份:

您可以使用Membership Class获取用户数据.

MemberShip.GetUser()提供有关用户的信息
MemberShip.GetUser().ProviderUserKey().ToString()返回用户ID

How to access data of registered user for Login?

Personally, I would look at implementing Membership: MSDN: Introduction to Membership[^]

you can use Membership Class to get User Data.

MemberShip.GetUser() gives Information about user
MemberShip.GetUser().ProviderUserKey().ToString() returns UserID