lib/janus/manager.rb
def login(user, options = {})
      options[:scope] ||= Janus.scope_for(user)
      set_user(user, options)
      Janus::Manager.run_callbacks(:login, user, self, options)
    end
def login(user, options = {})
      options[:scope] ||= Janus.scope_for(user)
      set_user(user, options)
      Janus::Manager.run_callbacks(:login, user, self, options)
    end
Logs a user in.

 FIXME: what should happen when a user signs in but a user is already signed in for the same scope?!