code: def handle_401(self, response, **kwargs):
          
  
          log.debug("handle_401(): Handling: 401")
          if _negotiate_value(response) is not None:
              _r = self.authenticate_user(response, **kwargs)
              log.debug("handle_401(): returning {0}".format(_r))
              return _r
          else:
              log.debug("handle_401(): Kerberos is not supported")
              log.debug("handle_401(): returning {0}".format(response))
              return response
docs: Handles 401's, attempts to use gssapi/kerberos authentication