code: def make_stream_features(self, stream, features):
          
          mechs = self.settings['sasl_mechanisms']
          if mechs and not stream.authenticated:
              sub = ElementTree.SubElement(features, MECHANISMS_TAG)
              for mech in mechs:
                  if mech in sasl.SERVER_MECHANISMS:
                      ElementTree.SubElement(sub, MECHANISM_TAG).text = mech
          return features
docs: Add SASL features to the <features/> element of the stream.
  
          [receving entity only]
  
          :returns: update <features/> element.