# File lib/googleauth/service_account.rb, line 151
      def initialize options = {}
        json_key_io = options[:json_key_io]
        if json_key_io
          @private_key, @issuer, @project_id =
            self.class.read_json_key json_key_io
        else
          @private_key = ENV[CredentialsLoader::PRIVATE_KEY_VAR]
          @issuer = ENV[CredentialsLoader::CLIENT_EMAIL_VAR]
          @project_id = ENV[CredentialsLoader::PROJECT_ID_VAR]
        end
        @project_id ||= CredentialsLoader.load_gcloud_project_id
        @signing_key = OpenSSL::PKey::RSA.new @private_key
      end