code: func (s *PresenceService) GetNamespaces() ([]services.Namespace, error) {
  	result, err := s.GetRange(context.TODO(), backend.Key(namespacesPrefix), backend.RangeEnd(backend.Key(namespacesPrefix)), backend.NoLimit)
  	if err != nil {
  		return nil, trace.Wrap(err)
  	}
  	out := make([]services.Namespace, 0, len(result.Items))
  	for _, item := range result.Items {
  		if !bytes.HasSuffix(item.Key, []byte(paramsPrefix)) {
  			continue
  		}
  		ns, err := services.UnmarshalNamespace(
  			item.Value, services.WithResourceID(item.ID), services.WithExpires(item.Expires))
  		if err != nil {
  			return nil, trace.Wrap(err)
  		}
  		out = append(out, *ns)
  	}
  	sort.Sort(services.SortedNamespaces(out))
  	return out, nil
  }
docs: // GetNamespaces returns a list of namespaces