The problem is more subtle than just authorisation.. you need some way to 'group' machines on a network. If you just use LAN broadcast/discovery, and you want

The problem is more subtle than just authorisation.. you need some way to 'group' machines on a network. If you just use LAN broadcast/discovery, and you want things to be automatic, then multiple users on the same network end up snuffling their way in to your mouse sharing configuration or you're bombarded with requests to connect. A pairing mode would solve this but then you have to train users to set it up, it's not "seamless", and Apple wouldn't have been able to do the cool demo. Synergy 2 used a cloud approach to pairing for the same reason