SetPage obsolete in forms 1.3 - how should we change the page after the main one has been loaded?

For login screens in my apps I have used this pattern https://github.com/conceptdev/xamarin-forms-samples/tree/master/LoginDemo
However now Forms 1.3 makes SetPage obsolete in favour of a main page property, which is fine for initially showing the login screen if necessary, but my question is how do I change the current page in Android apps at runtime?

For example, if I want to have a MainPage which has a logout button that shows the LoginPage. The way I previously did it was to call SetPage, but now that is obsolete what is the correct way to do it?