Architectural question

[eluser]i_am_using_ci[/eluser]
Hi, I got a problem while developing my application with CI:

I have admin class which handles some methods, also this class has internal login/logout methods, it's based on sessions.

The problem is: I wan't to deny usage of any method except login/logout to unauthorized users, how can it be done? I've tried to make some checks in __construct() and wrote internal library for this, but I got infitity redirect when I'm trying to redirect unauthorized user.

How can I fix my architectural problem?