How can I access the logged in user from outside of a controller?

I'm using SignalR to process clicks from the client on my MVC3 application.

Every time a user clicks something, I need to verify the logged in user.

If this were inside an MVC3 controller, I would go:

if (User.Identity.IsAuthenticated)
{
    string username = User.Identity.Name;

    //My code here.
}

However, this code execution is not inside a Controller class.

Basically, how can I access the logged in users name from outside a controller?