elt = self.element.find('sts:{}'.format(name), _STS_NS)
        return STSElement(self.root_name, elt) if elt is not None else None

    def get_child_text(self, name, strict=True):
        """Extract text of a child element. If strict, and child element is
        not present, raises InvalidXMLError and otherwise returns
        None.

        """
        if strict:
            try:

        """
        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