I\'m leaving old version of question on a bottom.
I\'d like to implement custom authentication for SignalR clients. In my case this is java clients (Android). Not we
In fact, accepted answer is wrong. Authorization attribute, surprisingly, shall be used for authorization (that is, you should use it for checking whether requesting authenticated user is authorized to perform a desired action).
Also, since you using incorrect mechanics, you don't have HttpContext.Current.User.Identity set. So, you have no clear way to pass user info to your business / authorization logic.
And third, doing that you won't be able to use Clients.User() method to send message to specific user, since SignalR will be not able to map between users and connections.
The correct way is to plug in into OWIN authentication pipeline. Here is an excellent article explaining and demonstrating in detail how to implement custom authentication to be used in OWIN.
I not going to copy-paste it here, just follow it and make sure you implement all required parts:
After you have these, register them into OWIN:
app.Map("/signalr", map =>
{
map.UseYourCustomAuthentication();
var hubConfiguration = new HubConfiguration
{
Resolver = GlobalHost.DependencyResolver,
};
map.RunSignalR(hubConfiguration);
});