code: func IsMember(c context.Context, groups ...string) (bool, error) {
  	if s := GetState(c); s != nil {
  		return s.DB().IsMember(c, s.User().Identity, groups)
  	}
  	return false, ErrNotConfigured
  }
docs: // IsMember returns true if the current caller is in any of the given groups.
  //
  // Unknown groups are considered empty (the function returns false).
  //
  // May return errors if the check can not be performed (e.g. on datastore
  // issues).