I want to offer a "highscore" list for friends in my app (at this point iPhone/iPad), so that if the user connected to facebook, he will get a list with his/her friends scores.

Connecting is easy, retrieving friends is easy, but figuring out the best way to store the scores is not.

As it seems I need to the store the scores on my own server server, no big deal. But what is considered a reasonable safe way to transfer the data? When communicating with facebook, authentication is clear - but communicating with my server basically anyone could post scores for another user if I send user id and score. Obfuscation might help a bit, but is there any better way to make sure that the data comes from the fb-logged-in person?

Scores can also go down, so changing scores for other persons won't necessary help them.

Thanks :)