"""Initialize STSElement from name and XML string data.

        :param name: Name for XML data. Used in XML errors.
        :param data: string data to be parsed.
        :return: Returns an STSElement.
        """
        try:
            return cls(root_name, cElementTree.fromstring(data))
        except _ETREE_EXCEPTIONS as error:
            raise InvalidXMLError(
                '"{}" XML is not parsable. Message: {}'.format(

        """
        if self.cid is not None:
            fetcher = self._create_credentials_fetcher()
            return RefreshableCredentials.create_from_metadata(
                metadata=fetcher(),
                refresh_using=fetcher,
                method=self.METHOD,
            )
        else:
            return None

    def _create_credentials_fetcher(self):
        method = self.METHOD

        def fetch_credentials():