May 27, 2016 09:02 AM|Fei Han - MSFT|LINK
According to your description, you’d not like to send message to all connecting users, you want to broadcast message to a specific set of users. So the following approaches will not meet the requirement.
Clients.All.NewMessage(message); //send message to all clients
Clients.Group(groupName).NewMessage(message); //according to your description, you could not use SignalR Group
SignalR also enable us to broadcast message to clients in these two ways.
Clients.Client(clientId).NewMessage(message); //send a message to a particular user, use this, you need to loop through user collection
Clients.Clients(clientIds).NewMessage(message);//use this, you need to pass a connection id list to method
As far as I know, it seems that SignalR enable us to send message to client in four ways as I mention, if both of them could not meet your requirement, I have no more solution.