Authenticating with Grape

api.rb

module Todo
  class API < Grape::API
    use Rack::Session::Cookie
    version 'v1', :format => :json
    
    helpers do
      def current_user
        return nil if env['rack.session'][:user_id].nil?
        @current_user ||= User.get(env['rack.session'][:user_id])
      end
      
      def current_user=(user)
        env['rack.session'][:user_id] = user.id unless user
        @current_user = user
      end
    end
    
    resource '/user' do
      post do
        User.create(params['user'])
      end
    end
    
    resource '/user' do
      http_basic do |username, password|
        current_user = User.authenticate(username, password)
      end
      
      get do
        current_user
      end
    end
  end
end

Yup, I too want to look at the implementation of the authenticate(username, password) method.
Especially what it returns.