Verifying an Android subscription in a Ruby on Rails app using the Google Play API

google_play_verification.rb

class GooglePlayVerification
  require 'google/api_client'
 
  # Refer: 
  # https://code.google.com/p/google-api-ruby-client/issues/detail?id=72
  # and
  # http://jonathanotto.com/blog/google_oauth2_api_quick_tutorial.html
  # and
  # http://milancermak.wordpress.com/2012/08/24/server-side-verification-of-google-play-subsc/
  GOOGLE_KEY    = 'xxx-xxx.apps.googleusercontent.com'
  GOOGLE_SECRET = 'xxx'
  ACCESS_TOKEN  = 'xxx'
  REFRESH_TOKEN = '1/4Qxxx'
  APP_NAME      = 'xxx'
  APP_VERSION   = '1.0.1'
 
  def self.google_api_client
    @@google_client ||= Google::APIClient.new(
      auto_refresh_token:  true, 
      application_name:    APP_NAME, 
      application_version: APP_VERSION
    ).tap do |client|
      client.authorization.client_id     = GOOGLE_KEY
      client.authorization.client_secret = GOOGLE_SECRET
      client.authorization.access_token  = ACCESS_TOKEN
      client.authorization.refresh_token = REFRESH_TOKEN
    end
  end
 
  # ie. https://developers.google.com/android-publisher/v1/
  # eg.
  # @package_name    com.stocklight.stocklightapp
  # @subscription_id com.stocklight.stocklight.standardsubscription
  # @purchase_token  xxx
  def self.verify_subscription(package_name, subscription_id, purchase_token)
    client = self.google_api_client
 
    # Verify whether the transaction_receipt is valid
    subscriptions = client.discovered_api('androidpublisher', 'v1')
    api_method = subscriptions.purchases.get
    purchases = client.execute(api_method: api_method, parameters: { 
      "packageName"    => package_name,
      "subscriptionId" => subscription_id,
      "token"          => purchase_token
    }).data
  end
 
end