How to implement session based user authentication in CodeIgniter?

[eluser]Unknown[/eluser]
Hi there i am noob to codeigniter and to the mvc pattern as well. I would like to build a login system, but i don't know where should i check the sessions in the code. The same goes for language selection, and to everything else that could lead to different types of views.

I mean coding the same logic in each controller for selecting the views based on users' authentication, or selected language etc... seems a weird solution to me. But coding this logic into a view template doesn't sound better.

How would you guys solve this?