class Google::Auth::DefaultCredentials

def self.determine_creds_class json_key_io
  json_key = MultiJson.load json_key_io.read
  key = "type"
  raise "the json is missing the '#{key}' field" unless json_key.key? key
  type = json_key[key]
  case type
  when "service_account"
    [json_key, ServiceAccountCredentials]
  when "authorized_user"
    [json_key, UserRefreshCredentials]
  when "external_account"
    [json_key, ExternalAccount::Credentials]
  else
    raise "credentials type '#{type}' is not supported"
  end
end