Feedback on session check, login system.

[eluser]überfuzz[/eluser]
I've got a login-system on a site. What would be the best practice of checking the session.

Prior to CI I checked in every file etc to be sure that the user had the right access level. Now, using CI, I've got a folder controllers/login wish is only open to users, logged in. Furthermore, I've got a MY_Controller fetching and passing stuff throughout the system.

Where should the control of the session be. My idea was to check in the MY_Controller and extend it to every controller. (The my-extension is ok sins every page will share header etc.)