I don't know where to start.  I want to have a simple authentication server.  All it will do is ask a user for their name and password so that they can access the internet.  That's all it will do.  If a user cannot supply a valid username and password, internet access will be blocked.
But I haven't got a clue where to start.  Please point me in the right direction.
Since this server will have no heavy-duty function, I prefer a GUI-based solution.  Simplicity in setup is important.  So a point and click option is preferable to a command line.