def METHOD_NAME(self, data_dict):
    """
    Parse unregister request from SPARCS SSO server
    :param data_dict: a data dictionary that the server sent
    :returns: the user's service id
    :raises RuntimeError: raise iff the request is invalid
    """
    client_id = data_dict.get("client_id", "")
    sid = data_dict.get("sid", "")
    timestamp = data_dict.get("timestamp", "")
    sign = data_dict.get("sign", "")
    if client_id != self.client_id:
        raise RuntimeError("INVALID_REQUEST")
    elif not self._validate_sign([sid], timestamp, sign):
        raise RuntimeError("INVALID_REQUEST")
    return sid