title: UserId in SignalR Core
body: <p>I'm using SignalR with ASP.NET Core 2.0 and I'm trying to send a notification for a specific user like this:</p>
  <pre class="lang-cs prettyprint-override"><code>_notification.Clients.User(id).InvokeAsync(&quot;SendMes&quot;);
  </code></pre>
  <p>where _notification is IHubContext.
  But it doesn't work. When I send the notification for all users, everything is fine and all users get the notification. But when I send it to a specific user, nothing happens. In connections I have needed user but it seems as if he doesn't have userId. So how can I do this? By access to Identity and claims? If so, how to do this?</p>