ruby-on-rails-3 - google-api-ruby-client 找不到类 PKCS12 和 JWTAsserter

Question

我收到以下关于 google-api-ruby-client 的错误：

NameError: uninitialized constant Google::APIClient::PKCS12 
NameError: uninitialized constant Google::APIClient::JWTAsserter

这是我的代码的概要：

require 'google/api_client'

class Commissions::GoogleAffiliateNetwork < ActiveRecord::Base

  def self.path_to_key_file
    Rails.root + 'config/xxx-privatekey.p12'
  end

  def self.passphrase
    'supersecretphrase'
  end

  def self.service_email
    '42@developer.gserviceaccount.com'
  end

  def api_auth_uri
    'https://www.googleapis.com/auth/gan'
  end

  def self.make_request(opts = {})
    key = Google::APIClient::PKCS12.load_key(path_to_key_file, passphrase)
    asserter = Google::APIClient::JWTAsserter.new(service_email, api_auth_uri, key)

    api_client = Google::APIClient.new
    api_client.authorization = asserter.authorize()
  end

end

在 Gemfile 中：

gem 'google-api-client'

我错过了什么吗？