public override async Task OnDisconnectedAsync(Exception exception)
{
_manager.User = Context.User;
DAL.Models.User user = _manager.Disconnect();
await Clients.Group(_manager.GetGroupIdentifier).SendAsync("userDisconnect", user);
await Groups.RemoveFromGroupAsync(Context.ConnectionId, _manager.GetGroupIdentifier);
await base.OnDisconnectedAsync(exception);
}
