def METHOD_NAME(self, element):
    """
    Parse challenge and send response from the mechanism.
    @param element: the challenge protocol element.
    @type element: L{domish.Element}.
    """
    try:
        challenge = fromBase64(str(element))
    except SASLIncorrectEncodingError:
        self._deferred.errback()
    else:
        self.sendResponse(self.mechanism.getResponse(challenge))