private async Task <IEnumerable <RsaKey> > DeleteRetiredKeysAsync(IEnumerable <RsaKey> keys) { var retiredKeys = keys.Where(_timeKeeper.IsRetired).ToArray(); foreach (var retiredKey in retiredKeys) { await _repository.DeleteKeyAsync(retiredKey.KeyId); } return(keys.Except(retiredKeys).ToArray()); }