web_service_dispatching_mode :layered

Hello All,
I am using layered dispatching with AWS. My controller looks like this:

  web_service_dispatching_mode :layered
  web_service_scaffold :invoke

  web_service :user, UserService.new

Here is the part of UserService that is failing (It's saying session
isn't an object):

class UserService < ApplicationController
  web_service_api UserApi

  def login(username, password)
    logged_in_user = User.login(username,password)
    if logged_in_user
      session[:user_id] = logged_in_user.id
      return true
    else
      return false
    end
  end
end

Can you use sessions with layered dispatching? If so, how? Do I need to
require a library manually? Using sessions worked with direct
dispatching (which I believe is SOAP, rather than XML-RPC). Thanks in
advance!