code: def send_challenge_response(self, response_plain):
          
  
          # Get a basic stanza body
          body = self.get_body()
  
          # Create a response tag and add the response content on it
          #   using base64 encoding
          response_node = ET.SubElement(body, 'response')
          response_node.set('xmlns', XMPP_SASL_NS)
          response_node.text = base64.b64encode(response_plain)
  
          # Send the challenge response to server
          resp_root = ET.fromstring(self.send_request(body))
          return resp_root
docs: Send a challenge response to server