docs: def get_group_dns(self):
          """
          Returns a (cached) set of the distinguished names in self._group_infos.
          """
          if self._group_dns is None:
              group_infos = self._get_group_infos()
              self._group_dns = set(group_info[0] for group_info in group_infos)
  
          return self._group_dns