I submitted an update which was rejected by Apple because I used Google Sign-In. I thought it was the obvious choice for authentication methods since all Pokemon GO users will have one and it didn't violate an app guidelines so I responded using the resolution center.

I got a call today from Apple and try as I might I could not convince them that my using Google Sign-In does not link to Niantic or the Pokemon Company and you don't need to use the same account you use for Pokemon GO or even have a Pokemon GO account to use my app. They said if I switch to Facebook login or created my own that would fix the problem.

The token I get from Google when a user signs-in does not allow me to connect to Niantic's API even if I wanted to but this was lost on the app reviewer.

I submitted an appeal to the review board and will post an update once its complete.