getConfirmXdsa method
Extracts the bound xDSA public key from the Confirm claim, or null if absent or a different key type.
Implementation
xdsa.PublicKey? getConfirmXdsa() {
final (kty, bytes) = _readConfirm();
if (kty != _algorithmIdXdsa || bytes == null) return null;
return xdsa.PublicKey.fromBytes(bytes);
}