I’ve also been adding Facebook integration.  So far the integration solutions for Unity3D that I’ve found so far have had huge security holes so I’ve had to come up with something myself. Not to say it doesn’t have holes either but at least I tried to keep people from hacking the app

What I’ve done is use the .NET Facebook API. I validate the Facebook user and look up their details in SimpleDB and put it all together in a class.  I serialize the class, RSA encrypt the bits salt and sign the data.  I send this as a cookie that gets picked up in the Facebook page and forwarded to Unity3D through JavaScript.

Unity3D takes this blob of data when establishing communication with the UDP server.  The server can then validate the signature, decrypt the data and viola.