// Get all WebHooks of a User for an Action. It is used to send Notifications against all actions of a User
        public override async Task <ICollection <WebHook> > QueryWebHooksAsync(string user, IEnumerable <string> actions, Func <WebHook, string, bool> predicate)
        {
            if (user == null)
            {
                throw new ArgumentNullException(nameof(user));
            }

            user      = NormalizeKey(user);
            predicate = predicate ?? DefaultPredicate;

            try
            {
                var registrations = await _webHookRepository.GetMany <Registration>(user);

                ICollection <WebHook> matches = registrations.Select(r => ConvertToWebHook(r)).Where(w => (MatchesAnyAction(w, actions) && predicate(w, user))).ToArray();
                return(matches);
            }
            catch (Exception ex)
            {
                var message = string.Format(CultureInfo.CurrentCulture, Constants.Constants.OperationFailed, "Get", ex.Message);
                _logger.Error(message, ex);
                throw new InvalidOperationException(message, ex);
            }
        }