如何存储Facebook用户ID以进行授权?

I'm using the Facebook api to let my users login/signup and if they don't have an account they create a new one, of if they already have an account they can connect the older with FB.

I did this for few years but recently i noticed my login button doesn;t work anymore, becays ei think they changed the users Id. is that correct?

what value should I store to be sure that user has a FB account and is the same user.

is the app_scoped_user_id good? are they gonna change again the ID?