Table-less UserSession "model" for Rails 3

UserSession.rb

# -*- encoding : utf-8 -*-
class UserSession

  include ActiveModel::Conversion
  include ActiveModel::Validations
  extend ActiveModel::Naming

  validates_presence_of :email
  validates_presence_of :password

  attr_accessor :email, :password

  def initialize(*args)
    attributes = HashWithIndifferentAccess.new(args.extract_options!)
    self.email = attributes[:email]
    self.password = attributes[:password]
  end

  validate do
    unless user.try(:authenticate, password)
      errors.add(:base, "Invalid email or password.")
    end
  end

  def user
    @user ||= User.find_by_email(email) if email
  end

  def persisted?
    false # always POST
  end
end