Would be nice if there was support for PKCS11 (hardware tokens, i.e. smart cards) in QSslSocket.
It looks like the original ticket (QTBUG-3705) was closed off originally back when it was Nokia... I'd like to revive this issue again to see what can be done to get PKCS#11 support into Qt (QML would be too good!!). There is a dead link in that ticket to an example on how to use QSslKey Opaque option, so the least that can be done is to provide an example of how to correctly use this option on the key...
The most I've been able to find on this matter is a qca plugin, which I'm unsure if it's still has pkcs11 support in qt5 or not. Either way, it may be a pipe dream, but figure someone should ask for support on this again.