The 6 digit number is TOTP, it's an RFC and has nothing to do with webauthn. Webauthn is basically what you are asking for (thumbprint). It's basically Apple's

The 6 digit number is TOTP, it's an RFC and has nothing to do with webauthn. Webauthn is basically what you are asking for (thumbprint). It's basically Apple's TouchID brought across platforms and across the Web.