    If your application requires that users sign-in to enable
certain functionality, pay attention to the user experience and
workflow around sign-in and sign-out. Try to keep your
application functional while the user is still signed-out.
Provide some default experience that still has value to the
user. If sign-out is not a common action (such as caching
credentials), implement the functionality via the settings
charm; this way it will not be intrusive, and the user will
intuitively find it consistent with other Windows 8 Metro style
apps.