'Handle notification that the server supports TLS.
Arguments:
features -- The stream:features element.'

def _handle_starttls(self, features):

    if ('starttls' in self.xmpp.features):
        return False
    elif (not self.xmpp.use_tls):
        return False
    else:
        self.xmpp.send(features['starttls'], now=True)
        return True
