The previous implementation would attempt to fetch groups using the end-user's Google auth token. This only worked for admin accounts, or users with 'delegated' access to the `admin.directory.group.readonly` API.
This commit changes the approach to use a single 'service account' for fetching the groups. This removes the need to add permissions to all regular user accounts. I'll be updating the [meta docs](https://meta.discourse.org/t/226850) with instructions on setting up the service account.
This is technically a breaking change in behavior, but the existing implementation was marked experimental, and is currently unusable in production google workspace environments.
This commit introduces a new site setting "google_oauth2_hd_groups". If enabled, group information will be fetched from Google during authentication, and stored in the Discourse database. These 'associated groups' can be connected to a Discourse group via the "Membership" tab of the group preferences UI.
The majority of the implementation is generic, so we will be able to add support to more authentication methods in the near future.
https://meta.discourse.org/t/managing-group-membership-via-authentication/175950
