How to access native app for Facebook login?

Hi,

I've implemented the code below for FB login but it pops a browser and asks user to provide email and password.

    void LoginToFacebook ()
    {

        var auth = new OAuth2Authenticator (
            clientId: "XXXXXXXX",
            scope: "email,user_likes",
            authorizeUrl: new Uri ("https://m.facebook.com/dialog/oauth/"),
            redirectUrl: new Uri ("http://www.facebook.com/connect/login_success.html"));

        // If authorization succeeds or is canceled, .Completed will be fired.
        auth.Completed += LoginComplete;

        UIViewController vc = auth.GetUI ();
        PresentViewController (vc, true, null);
    } 

I was expecting to access to native Facebook app instead of browser display.

Is there anyone who knows how I can trigger native FB app and gets authentication?

Thanks in advance.