title: SignalR - Send message to user using UserID Provider
body: <p>Using SignalR, I believe I should be able to send messages to specific connected users by using <a href="http://www.asp.net/signalr/overview/signalr-20/hubs-api/mapping-users-to-connections#IUserIdProvider" rel="noreferrer">UserID Provider</a></p>
  
  <p>Does anyone have an example of how this would be implemented? I've searched and searched and can not find any examples. I would need to target a javascript client.</p>
  
  <p>The use case is, users to my site will have an account. They may be logged in from multiple devices / browsers. When some event happens, I will want to send them a message.</p>