Google Sign in usage
- it's disabled by default
- the client ID can be changed in the 'Settings->System configuration->Google client ID for Google Sign in'
- the G button can be disabled in the 'Settings->System configuration->Don't display Google Sign in button'
- the Google account's email is used as a key in GUI's user list. So you need to create users in the GUI with the appropriate email and to use the 'Google Sign in' as an authorization engine. The user's permissions are used from the GUI's user setting.
- click on the G button an do auth
Own credential (the fast way how to create own credential)
- Your own credentials will you create via https://console.developers.google.com (It supposes you can use the developer console)
- API & Service -> credential -> create new credential -> type 'OAuth client ID' -> web application: here you get your client_id which you enter into the GUI.
- Return to the API -> credentials -> OAuth consent screen : set 'Application type' and 'Authorized domains'
That's all. After that logout from all your services logged with google account a re-login.
(Of course don't forget to enable the GAuth in the GUI).