A search on Google led me to Chillster's Facebook SDK at http://forum.unity3d.com/threads/facebook-sdk-for-unity-plus-windows-phone-8.217907/ . It was free and also fairly new. I had a fair bit of trouble getting it to do what I wanted because of limitations I wouldn't accept, and because of my interpretations of the instructions. Ultimately I got it working. Here's a walkthrough I would have presented:
1. First you need to add your Windows Phone 8 app to your Facebook developer dashboard. Do this by going to https://developers.facebook.com/ and clicking on Apps at the top. If your app doesn't exist, use Create a New App and fill the proceeding form out.
2. If your app already exists (like you wrote your game for iOS/Android first), you still need to set it up. On the left side of the app's dashboard page on Facebook is a menu item for Settings. Click on it. Hidden beneath your existing platform listings is a "+ Add Platform" button. I swear I went to this page half a dozen times and never saw that button. Click on it and add your app product ID (which you get from your Windows Phone Dev Center account) to the second line. Remove the dashes and make sure you don't have curly brackets.
I had to install the Facebook app on my phone before I could use Facebook integration.
1. Add Chillster's Facebook SDK asset to your Unity project (or better yet make a test project).
2. Look up at your Unity menu bar (File, Edit, Assets...). There should now be a Facebook menu. Go there and choose "Edit Settings" and fill those out.
3. Now go to the link I mentioned at the start of this section (http://forum.unity3d.com/threads/facebook-sdk-for-unity-plus-windows-phone-8.217907/ ), and read Chillster's official documentation for getting set up starting with step 2.1. You've already done step 2.3, so you can skip that step.
My goal was to make it so users could send app requests to friends which invited them to download my game. So when I found this in the code comments:
"... throw new UnityException("There is no Facebook AppRequest on Windows Phone 8"); ... "
I thought it was just an asset limitation. For a while I tried using FB.API() to get the job done starting with getting a friends list. I simply could not get that to work until I finally called "FB.API("me\friends"...)" (note the direction of the slash), and making sure to include the "user_friends" permission at the login. Then I tried a number of ideas to send an app request by using FB.API(); all failed. I ultimately settled for just doing a post on a player's feed by calling:
var wwwForm = new WWWForm(); wwwForm.AddField("link", "http://www.gamieon.com/hamsterchase"); wwwForm.AddField("linkName", "Hamster Chase for Windows Phone 8!"); wwwForm.AddField("linkCaption", myCaption); FB.API("me/feed", Facebook.HttpMethod.POST, fb_OnFeedComplete, wwwForm);
It doesn't show the link name or caption in my feed; but I'm going to leave those in anyway in case they someday appear through either asset or Facebook-side updates.
I ultimately released Hamster Chase with Facebook integration. It works for posting to Facebook feeds, and it was nice to see it work without having to publish the game first (unlike other assets I integrated with). I'm sure it won't be long before future versions of Facebook integration assets are released with easier setups and more features; including app requests.