Facebook e-mail as user_id for accessing documents

[Andrew Tokarev]

Am I right that Facebook user's e-mail is used to identify users when we giving access to some channel in SyncGateway's sync function?

I can't present a test case so far but it feels like that user can change his facebook's e-mail and try to pull the docs using new session and new e-mail (all old docs will be lost, not accessible for sync)

Can we use Facebook's user_id instead of e-mail?