[mths]

Although when setting this up, Gmail really make you feel like they might pull support at any minute.

I wonder if Fastmail could log you in to Gmail in a way that's consistent with Google's security model, similar to how you can "log in with Google" on many services. I'd much prefer it over the app password thing.

[archb]

Now that you mention it, I remember that's how Fastmail works today. They use app passwords for non-Google-hosted email inboxes, and 'login with Google' for Google-hosted inboxes.