On Wp 8 - LoginAsync showing facebook login page even if Already logged into the facebook app

[suresh-s]

We are using LoginAsync on our Wp8 app. Even if user already loggedinto the installed Facebook app on wp8, LoginAsync method call still showing facebook login page.

 We are developing cross platform smart phone apps.   in IOS (FBSession openActiveSessionWithReadPermissions:) call do the following.

1. if facebook app is not yet installed, it shows the facebook web login page (not asking to install the facebook app).
2. If facebook app is loggedin, it gets the access token from the facebook app and shows only permission page (Not shows login page since user already logged in facebook app)

We want the same behaviour in WP8 also.

How can i achieve it in WP8? LoginAsync method call always shows facebook login page.