If you sign into Pokémon Go on iOS, you may be giving it more access than it needs.
A word of warning if you're playing Pokémon Go on iOS: signing into the app through Google currently gives the game full access to your Google account hat tip to Adam Reeve for discovering the issue .
External apps that you sign into with Google often ask for a small subset of permissions based on what they need to do—view your contacts, view and send e-mail, view and delete Google Drive documents, and so on.
But Niantic's Pokémon Go iOS app doesn't ask, and with full account access, it can theoretically do all of those things and more.
You can check on and revoke permissions for Pokémon Go and any other external app on this page.
We've independently verified that the game requests full account access on iOS, but the Android version doesn't appear to have the same problem; you can sign in with Google but the app doesn't show up on the permissions page.