One of the things you might need Twitter authentication in your app for is to be able to share photos. In my last article, I described the way to get the user authenticated (PIN based authentication), and this article will show one of the methods for sharing photos on Twitter from Windows Phone app. Note that there are of course other solutions, this is just my way of handling it in my apps.
Just like with Facebook, sharing statuses on Twitter from Windows Phone app can be simply accomplished using ShareStatusTask launcher. A more complicated scenario is when you want to share a photo on Twitter. In order to do that, you first need to authenticate the user from your app to allow your app to communicate with Twitter and then to upload photos. This article will show you how to do the authentication part.