ASP .NET Authentication script

create a ASP VB .NET project which manages user accounts with a MS-SQLServer. the script will be communicating with an app on mobile phones. the app communicates via HTTP requests with the ASP script. before an app-user is able to access e.g: "[login to view URL]" he needs to have logged in. when the user has logged in the database will be informed about that (currentSessionHash). in the app code i want to be able to make a "secured" HTTP call like this: [login to view URL][xyzxyzxzy]&query=print. this query only returns the value is the user_session is valid. a user account can be: -registered -authenticated (loggedIn) -deauthenticated (loggedOut) -removed *there must be an automatic detection if a user disconnected without logging-out. (timeout, invalidate session) *there must be a function which determines if a given username/ID is logged-in. this is how i imagine the users table: USERS ID, Username, PasswordHash, LoggedIn, currentSessionHash > VB. NET preferred