def add_group_member(self, grp_name, user):
        """
        Add the given user to the named group.

        Both group and user must already exist for this to succeed.

        Args:
            name (string): Name of group.
            user_name (string): User to add to group.

        Raises:
            requests.HTTPError on failure.
        """
        self.project_service.set_auth(self._token_project)
        self.project_service.add_group_member(grp_name, user)