title: How to behave after correct login in WP app
body: <p>What is the proper way of handling application's behavior, after correct login?
  Let's imagine the following mechanism - user lands on the login page when the user setting key value is set to "false". Once the user performs login, he is navigated to main page. Everything works well, until the time, the user presses hardware "back" button. 
  Then he is navigated to the login page again. 
  My first thought was - well, lets check if the user is logged in using onNavigatedTo method, but apparently this makes the "back" button override its navigation purpose, which is subject to rejection during submission process.
  So I tried with removing navigation history, once the user is navigated to the main menu. But I am not sure whether this solution is fine. Is there some native solution, that I should look at? Looking forward to seing opinion ofsomeone more experienced in c#.</p>