title: React-Native Authentication Login with Token AsyncStorage
body: <p>I have 2 pages, a login, and a home. I use react-navigation to navigate between screens.
  When I will log in I post my username and password and get the token from the response.
  How to set the default screen in Home when in async storage there's a token. And when there's no token will automatically redirect to login, and also when logged in it'll no able to go back to the login screen.
  Thanks</p>