Setting up a proper NavigationPage

So I have a Login screen. When the user clicks login, I am doing the following from my Login page view model.

        Globals.NavigationPage = new NavigationPage(new Main());

        Device.BeginInvokeOnMainThread( () => {
            Globals.LoginPage.Navigation.PushModalAsync(Globals.NavigationPage);
        });

where Globals is a static class.

Is this correct? Is there a better pattern to use?