beeu_sinatra.rb

#UserService for GoogleAppEngine JRuby Sinatra apps
#Based on Ola Bini's Beeu

require 'java'
module US
  import com.google.appengine.api.users.UserServiceFactory
  Service = UserServiceFactory.user_service
end
def current_user
  if US::Service.user_logged_in?
    return US::Service.current_user
  else
    return false
  end      
end  
def logged_in?
  US::Service.user_logged_in?
end
def admin_logged_in?
  US::Service.user_logged_in? && US::Service.user_admin?
end
def login_url url=request.path_info
  US::Service.create_login_url(url)
end
def logout_url url=request.path_info
  US::Service.create_logout_url(url)
end
def require_login
  redirect US::Service.create_login_url(request.path_info) unless US::Service.user_logged_in?
end
def require_admin  
    redirect US::Service.create_login_url(request.path_info) unless US::Service.user_logged_in? && US::Service.user_admin?
end  

usage.rb

get '/secret' do
  require_login
  "hehe, you are logged in for this!"
end

get '/user_profile' do
  require_login
  @user = current_user  
  "Hello There "+ @user.getNickname + " with email " + @user.getEmail
end