[eluser]Narkboy[/eluser]
Always keep it simple! If your auth code controls access to the functions within the controller, then run it in the constructor and you're done.
If the auth code controls access to other controllers or to other assets, then I would probably place it into the constructor of a library, and auto-load the lib. I try to avoid hooks and have never needed to have one yet.
More detail on what the auth code does would help to understand exactly what you're after!
GL!