From the user perspective, I think that's an interesting idea. As long as it's an alternative login for the same account, not the only way to log in, that would seem a reasonable option to me.

But if you're going to add in OAuth capabilities, then GitHub and other OAuth providers would be good as well -- GitLab, for example. I have a feeling that more monks would want to use GitHub or GitLab as the OAuth provider for logging in here rather that Google, or at least want that as an option when configuring multiple OAuth providers.

Dunno if we'd need a way for a user to clear those.

Definitely. Being able to disassociate an external login provider would be essential ("someone hacked my Google account, and I don't want them to be able to log in as me here")