How to determine authenticated status on client side?

Do you know any syncronous way to get IsAuthenticated status for currentRequest in client side via javascript?

I can get current user via client model, but it will be asynchronous.

this.authenticationPending = true;
this.isAuthenticated = false;

ExecuteOrDelayUntilScriptLoaded(Function.createDelegate(this, function() {
   var context = new SP.ClientContext.get_current();
   this.website = context.get_web();
   this.currentUser = website.get_currentUser();
   context.load(currentUser);
   context.executeQueryAsync(
      Function.createDelegate(this, function ()
          {
             this.authenticationPending = false;
             this.isAuthenticated = this.currentUser.get_id() > 0;
          }),
          Function.createDelegate(this, function ()
          {
             this.authenticationPending = false;
             this.isAuthenticated = false;
          }));
}), "sp.js");

After that I can get status, but I need to get status synchronous.