Controller question

[eluser]Joozt[/eluser]
We are building a windows application witch connects to a (web) server using URL's.

The thing is you have to be logged in to use controllers, so the idea is to build a login module witch checks username and password and creates a SessionID, witch is stored in the database with the username.

So when running some other function the URL will always be: base_url()/Controller/function/username/sessionID/functionVariable/

But i don't want build every controller function with 2 variables called $username and $sessionID I just want the controllers to start picking there variables from the 3 segment.

Does anyone know if i can just change some settings or an easy way to do this?

Thanks alot in advance!