Controller - Extend so user is/isn't authorized with reactive computation.

gistfile1.js

MyController = RouteController.extend({
  before: function () {
    var onReady = function () {
      if (/* whatever */)
        this.render();
    };

    var onWait = function () {
      // maybe show a loading or logging in function.
    };

    if (Meteor.user()) {
      return this.wait(userDataSubscriptionHandle, onReady, onWait);
    } else {
      this.render('notAuthorized');
      this.stop();
    }
  }
});