Is a Facebook proxymail email address unique for a visitor and app combination?

I am working on an app to allow users to log in to our website using Facebook. We also have an existing login system in place, which I would like to keep using as well. The objective is to save new Facebook users in our user database and merge existing users if they decide to login through Facebook from now on.

My app asks for the email permission, and I noticed there was a possibility for the user to use a xxxx@proxymail.facebook.com address. For the purpose of not creating duplicate user records, I would like to know if this proxyma开发者_Python百科il address is unique for a user + app combination.

In other words: if the user disallows my app and then re-allows it, will this user get a new proxymail address or will it stay the same through the lifetime off my app and the user?

The proxy emails are legacy. Any new user will have a cleartext email. I think you need to detect a proxy email from a previous user then issue a DELETE to /USERID/premissions to revoke their authentication and have them reauthorize your app. Then you will get their plaintext email. There is no way to convert all the legacy proxy emails to plaintext.