Xamarin.Auth with Twitter, keep getting "401 unauthorized"

Hi,

I'm relatively new with Xamarin and C# in general but it's getting better.

I just successfully integrated Xamarin.Auth in my application for Facebook, but I don't seem to succeed in getting it to work with Twitter. As I read on the forums I should use OAuth1 for Twitter and specify whatever callback url I want (I don't need it but you can't pass nothing as callback url for OAuth1).

So this is what I have, but I always get the error below (check screenshot).

var auth = new Xamarin.Auth.OAuth1Authenticator (
    "uyyoZd6cMXs0iZOqLHz7w", "o1XrijSGY8wJQK809ejKyuZbuXIGbItnCBAnpHChB0",
    new Uri ("http://api.twitter.com/oauth/request_token"),
    new Uri ("http://api.twitter.com/oauth/authorize"),
    new Uri ("http://api.twitter.com/oauth/access_token"),
    new Uri ("http://dev.twitter.com"));

auth.Completed += (s, eventArgs) => {
    this.DismissViewController(true, null);

    if (eventArgs.IsAuthenticated) {
        // Authenticated!
    }
    else {
        // Cancelled
    }
};

UIViewController authVC = auth.GetUI ();
authVC.ModalTransitionStyle = UIModalTransitionStyle.FlipHorizontal;

this.PresentViewController (authVC, true, null);

Someone that got Xamarin.Auth working with Twitter?
I can't seem to find examples and I can't get it to work like this :(.

Kind regards,
Wouter