Two weeks ago I had an update rejected because we decided to remove Login with Facebook from our app. The plugin that provides that support to Cordova is a dependency nightmare and not many people used it anyways so we removed it during a bugfix and dependency update. We got flagged for only supporting Google as a 3rd party login and basically forced to implement Apple ID sign in to release our fixes. Since adding support we've been further held up from releases because we require an existing account for Apple ID sign in to work and they rejected us for not allowing the QA account to sign in, while completely disregarding the use of the QA user account and password that we've always provided for the review process.
tl;dr Because of the broken App Store review process we've just removed 3rd party auth support from our app, which is a shame because it's a really slick sign in experience, but we don't want to deal with bugfix releases being held up in review.