Fix security key problems

For setup, see Log in with a hardware security key. There’s no macOS or iOS build yet.

What works where

	Linux desktop	Windows desktop	Android
Reaching the key	USB	USB, NFC and Bluetooth, through Windows’ WebAuthn (Windows 10 1903 or later)	USB-C and NFC
Make ecdsa-sk and ed25519-sk keys	yes	yes	yes
Log in with them	yes	yes, in Windows’ own dialog	yes, holding the key to the phone
Store the key on the security key	yes	yes	yes
Load stored keys from it	yes	only as administrator	yes
Import an id_ecdsa_sk / id_ed25519_sk file	yes	yes	yes

ecdsa-sk works with every FIDO2 key. ed25519-sk needs one with EdDSA (YubiKey firmware 5.2.3 and later, recent SoloKeys and Nitrokeys).

When something fails

Message starts with	Means
No security key found	Nothing was plugged in, or held to the phone, in time.
This computer does not let Sternway open the security key / Android did not allow …	Linux udev rules are missing; on Windows, raw access without administrator rights; on Android, the USB permission was refused.
More than one security key is plugged in	Making and loading keys need exactly one key.
Wrong PIN / … locked … / Too many wrong PINs in a row	Wrong PIN. A locked PIN can only be reset, which erases the keys stored on it. After three wrong in a row, unplug the key and plug it in again.
This security key has no PIN	Set one with the maker’s app.
The security key was not touched in time	Touch it while it blinks (about 30 seconds).
This security key cannot make this type of key	It lacks EdDSA. Use ECDSA.
This security key does not hold this key	The key file was made on another security key.
… cannot list the keys stored on it	The key is older than FIDO 2.1. Import the key files instead.