Restricted Domain

I don't think you can restrict multiple domains; at least according to the docs not BUT it does look like you can restrict to accounts owned by a Google Cloud Organization according to the docs: https://developers.google.com/identity/openid-connect/openid-connect#hd-...

I have not tested it but setting it to * should cover that.

The problem is that I can't use a wildcard because there are domains that I am not allowed to enable, so I need to allow login for specific domains only. It would also be a good solution for me if I use multiple APIs or if there are multiple buttons that users can use to authenticate. But if this cannot be resolved this way, then I need to look for another solution.

From Google's docs it doesn't look like that's an option, that link describes a single domain or wildcard only.

But maybe there is a way to add a validation step prior to Drupal allowing the authentication to create the user account, ie just at the stage where Google has returned the authorised email to bail out there. Haven't explored that myself though.

I would be happy to help with the testing if it’s not too complicated to integrate this feature into the module.