code: func (db *SnapshotDB) IsMember(c context.Context, id identity.Identity, groups []string) (bool, error) {
  	// TODO(vadimsh): Optimize multi-group case.
  	for _, gr := range groups {
  		switch found, err := db.isMemberImpl(c, id, gr); {
  		case err != nil:
  			return false, err
  		case found:
  			return true, nil
  		}
  	}
  	return false, nil
  }
docs: // IsMember returns true if the given identity belongs to any of the groups.
  //
  // Unknown groups are considered empty. May return errors if underlying
  // datastore has issues.