code: func GetCAByUniqueID(c context.Context, id int64) (string, error) {
  	cached, err := mappingCache.Fetch(c, func(interface{}) (interface{}, time.Duration, error) {
  		val, err := LoadCAUniqueIDToCNMap(c)
  		return val, time.Minute, err
  	})
  	if err != nil {
  		return "", err
  	}
  	mapping := cached.(map[int64]string)
  	return mapping[id], nil
  }
docs: // GetCAByUniqueID returns CN name that corresponds to given unique ID.
  //
  // It uses cached CAUniqueIDToCNMap for lookups. Returns empty string if there's
  // no such CA.