code: def _plain_authentication(self, login, password, authz_id=b""):
          
          if isinstance(login, six.text_type):
              login = login.encode("utf-8")
          if isinstance(password, six.text_type):
              password = password.encode("utf-8")
          params = base64.b64encode(b'\0'.join([authz_id, login, password]))
          code, data = self.__send_command("AUTHENTICATE", [b"PLAIN", params])
          if code == "OK":
              return True
          return False
docs: SASL PLAIN authentication
  
          :param login: username
          :param password: clear password
          :return: True on success, False otherwise.