There were news circulating on the internet regarding Pokemon Go take all your Google account information (Gmail, Google Drive, Google Document) during login permission being granted. You can safely disregard the circulated information, because Niantic has fixed it. Beside, it was happened on iOS devices only, since the apps launched we installed it on Android devices and didn’t see that permission being granted from our Google account from Pokemon Go.
There were minor error happened on iOS devices where Pokemon Go request full information from user’s google account, but that were fixed after that according to Niantic official announcement. If you are still worried that Niantic taking all your Google Account information, here is how you can check.
Login go your Google Account (via gmail or etc) and click here to find out what application has been connected to your Google account.
A quick look on it, we do not see the Google Account we used to login Pokemon Go has granted anything from Google Account.
If there any services connected to your Google Account and you are not happy with it, you can click on Remove to revoke the access from application has been granted earlier.
Conclusion, your Google account information is safe. Happy Pokemon Go!