def add_user_role(self, user, role):
        """Add role to given user.

        Args:
            user (string): User name.
            role (string): Role to assign.

        Raises:
            requests.HTTPError on failure.
        """
        self.service.add_user_role(
            user, role,
            self.url_prefix, self.auth, self.session, self.session_send_opts)