i got one more reject
"Hello,
Thank you for your resubmission.
In order to use Facebook for authentication even if it is optional, your app must include significant account-specific functionality from Facebook. Using users’s Facebook for account creation/authentication do not fall in to significant about specific features."
In rule saids: (ii) If your app doesn’t include significant account-based features, let people use it without a log-in. Apps may not require users to enter personal information to function, except when directly relevant to the core functionality of the app or required by law. If your core app functionality is not related to a specific social network (e.g. Facebook, WeChat, Weibo, Twitter, etc.), you must provide access without a login or via another mechanism. Pulling basic profile information, sharing to the social network, or inviting friends to use the app are not considered core app functionality. "
I repeat my question What is meant by "account-specific functionality from Facebook" ?