We don't know how to correctly use these identities. In particular, some
identities store parts of their private key material in certificate
extensions to work around hardware limitations. Not understanding these
extensions could lead to encrypting with the wrong protocol and
violating security assumptions.
Some SmartCard readers report this error when no SmartCard is inserted,
so we need to check for it when filtering for connected YubiKeys (along
with `pcsc::Error::RemovedCard` which some _other_ SmartCard readers
report instead).
Closesstr4d/age-plugin-yubikey#81.
Jack Grigg