How to protect all controllers under a module

HI everyone, I'm new to rails, and I have a little question.

I got tree modules, Admin, xml and flash.

I added a before_filter in my application.rb too check if the user is
authenticate. That work great. But when I did that, I had just one
module, the admin one!

Now I would like to apply this filter only on the admin section of my
site( So on the module admin)

How can I do that?

Thanks for any help

Sorry for the bad english!