Почитайте в MSDN Security Guidelines и информацию о Membership, Forms Authentication и Roles Management.
Все это, в той или иной степени, будет в любой книге об ASP.NET.
The difficult I’ll do right now. The impossible will take a little while. (c) US engineers in WWII
I don't always know what I'm talking about, but I know I'm right. (c) Muhammad Ali