# File lib/googleauth/service_account.rb, line 98
      def apply! a_hash, opts = {}
        # Use the base implementation if scopes are set
        unless scope.nil?
          super
          return
        end

        # Use the ServiceAccountJwtHeaderCredentials using the same cred values
        # if no scopes are set.
        cred_json = {
          private_key:  @signing_key.to_s,
          client_email: @issuer
        }
        alt_clz = ServiceAccountJwtHeaderCredentials
        key_io = StringIO.new MultiJson.dump(cred_json)
        alt = alt_clz.make_creds json_key_io: key_io
        alt.apply! a_hash
      end