public async Task <int> SubscribeForNotifications(string operationId)
        {
            await Groups.AddToGroupAsync(Context.ConnectionId, operationId);

            return(LongRunningOperation.GetCurrentProgress(operationId));
        }
 public Task CancelProcessing(string operationId)
 {
     Clients.Group(operationId).SetMessage("Cancellation Requested...");
     LongRunningOperation.CancelProcessing(operationId);
     return(Task.CompletedTask);
 }