Code Iginter Core subclassing

[eluser]Daniel Peraza[/eluser]
Well may be it's just me the one confused, so let me explain better my idea.

My application is a backend application, so I should not grant access to non-administrator users. Hence, I must check on every controller if the user has privileges enough to access to the system before I grant permissions to execute the requested action, right?, so far, this is the classic problem on user authentication. But taking this approach I fear to have to write repeated code on all my controller's constructors, so I prefer to have a single controller with authentication code centralized on it. If all the requests pass through this check, I'd expected the access to be denied to whom (for example) the session time limit expired (please correct me now if I'm wrong on this), or for those users trying to access to a site URI directly without authenticating their selves before.

Am I just misunderstanding the problem or am I right and you get the idea?.