class Google::Auth::UserRefreshCredentials

def self.read_json_key json_key_io
  json_key = MultiJson.load json_key_io.read
  wanted = ["client_id", "client_secret", "refresh_token"]
  wanted.each do |key|
    raise "the json is missing the #{key} field" unless json_key.key? key
  end
  json_key
end