Azure mobile HTML5 application - facebook authentication on iPhone in app mode

I have an HTML5 application that uses Azure mobile authentication to login (straight from the example code...provided below). It works fine in all desktop browsers and iPhone in Safari.  But from app / full screen mode, it does nothing (doesn't ask for permission to show a popup window like it does in safari and no popup windows shows up) and I can wait forever and nothing happens.  If I invoke it a second time, it gives an error saying "Error: Unexpected failure"...perhaps because the 1st attempt is still running?  Can anyone provide some assistance?  Thanks.

client.login("facebook").done(function (results) {
         alert("You are now logged in as: " + results.userId);
    }, function (err) {
         alert("Error: " + err);
    });