The Fair Email FAQ [1] states that it supports Google's OAuth, so why don't you authenticate with that?
"OAuth for Gmail is supported via the quick setup wizard. The Android account manager will be used to fetch and refresh OAuth tokens for selected on-device accounts. OAuth for non on-device accounts is not supported because Google requires a yearly security audit ($15,000 to $75,000) for this. You can read more about this here [2]."
"OAuth for Gmail is supported via the quick setup wizard. The Android account manager will be used to fetch and refresh OAuth tokens for selected on-device accounts. OAuth for non on-device accounts is not supported because Google requires a yearly security audit ($15,000 to $75,000) for this. You can read more about this here [2]."
1. https://github.com/M66B/FairEmail/blob/master/FAQ.md#user-co... 2. https://www.theregister.com/2019/02/11/google_gmail_develope...
So it maybe works, or maybe not, because they're not paying Google for the security audit.