Jeff Frederick

@chris2511 , if you need some Yubikey's, I can send you some. Contact me privately with a mailing address.

Good point, they might still be using the FIDO U2F API and not the WebAuthn API. I'll open a support ticket and ask. They "could' be using WebAuthn and are...

I just realized. I am pretty sure that Fastmail implemented WebAuthn. I can login the Fastmail iOS app on my iPhone using my YubiKey 5Ci. Since iOS ONLY supports WebAuthn...

Joel, can you post your Fastmail support ticket number here? We can then all open a support ticket with Fastmail and request that they add you to the "approved" OAuth...

OAuth is a Federated Authentication framework, think login with Google or Apple. Based on my conversations with FastMail, OAuth is how they allow 3rd party clients to authenticate using WebAuthn/FIDO...