Setting a PIN cannot be undone

[xi]

• YubiKey Manager (ykman) version: 4.0.9
• YubiKey model and version: YubiKey 5 NFC

I can set a FIDO PIN by running ykman fido access change-pin. I can later change the PIN by running the same command again. But there is no way to remove the PIN again.

As far as I understand, this is a limitation of the CTAP protocol. Still, ykman should document that limitation. Specifically, it should:

• Warn users that this action cannot be undone
• Explain what exactly will happen, so users can make an informed decision if they want to do it anyway
• Provide recovery options, e.g. explain how to use ykman fido reset and what other effects it has