"Passwordless login" via Passkey support for login and decryption

[tomfitzhenry]

It'd great if etesync supported passwordless login via Passkeys, in the same way that Bitwarden can do, as described in https://bitwarden.com/blog/log-into-bitwarden-with-a-passkey/

The end result would be users could login via either:

• their master password (as is the status quo)
• their passkey, which would perform usual FIDO2 auth, but also use the hmac-secret functionality to derive a symmetric key to decrypt the encrypted master password (stored on the server)

The benefit is that passkeys are phishproof (due to mutual auth) and are 1-click login.

Users that prefer to solely use passwords are unimpacted.