kscreenlocker works with shadow passwords and krb5 authentication, but fails when entering a PIN for a smartcard. KDM works with the PIN when logging in. kcheckpass calls pam_pkcs11 but fails with a "kcheckpass[xxxx]: no suitable token available" error. This is on an openSUSE Leap 15 install, and seems to be running: kcheckpass-5.12.5-lp150.1.1.x86_64.debug Is this a kcheckpass issue? Maybe PAM? But PAM works otherwise. The smartcard reader flashes when trying to unlock, so the basic plumbing seems to be okay.
kcheckpass support has been removed for a couple releases now.