Nice … I also want to know this…
You can't. Why do you want to do this? This probably means that this code you are trying to call should either be part of one of your models or in a module you can include in both controllers.
You should redirect them to the login page if they need to be logged in
You can either put them in a module as has already been mentioned, and
then include them in your controllers, or you can put them in helpers/
application_helper, or you can put them in ApplicationController as
all your other controllers subclass this, meaning they would
automatically inherit them.