Our app relies entirely on the current_user helper method (found in our ApplicationController) to retrieve the User object associated with the currently logged-in user (if any). You guys are using the devise gem for authentication, but you still have a current_user helper method which is made available to ApplicationController (and all subclasses).
Normally, the current_user method looks something like this:
def current_user
# do some magic to get the user id from the (encrypted) session cookie…
user_id = get_user_id_from_session