How to get handle to the user through AuthLogic

I am having user_session.rb which extends the Authlogic as follows

class UserSession < Authlogic::Session::Base
  def to_key
    new_record? ? nil : [ self.send(self.class.primary_key) ]
  end
end

I am trying to override the save method from
Authlogic::Session::Existence. How to refer the current_user in this
method? Since i like to override the authlogic methods to do some
additional checks.