Xamarin.Forms change page after login properly?

Hello.
I am making an application with Xamarin.forms and currently I have my mainpage set to the login page in the start of the application. The Login page is just set with a default navigationpage, because there is some navigation between login page and register page. It is done so in the App.xaml.cs

        MainPage = new NavigationPage(new MainPage())
        {
            BarBackgroundColor = Color.FromHex("#FFFF00"),
        };

When I then ensure the login credentials is correct, I want to switch my MainPage to my Masterdetailpage. I have tried to do it so:

Application.Current.MainPage = new NavigationPage(new FrontPageMaster());

Now the problem is, when I do it this way, on my android application it wont show my menu icon, and I will just get a completly blank navigation bar. If I on the other hand just sets the Masterdetailpage from the start at the application launch, I will get the navigation bar menu hamburger icon shown. Anyone has a solution to this? I will prefer not to push the loginpage on as a modal stack as you can go back with the hardware button on android and I don't like to disable those as I want the user to be able to use them.

Thanks a lot - Filip.