The active ingredient in the cackey package is the file
/usr/lib/pkcs11/libcackey.so - which is a "PKCS #11 module".
Its usage depends on application to support it. It's similar in concept
to a PAM module or an NSS module.

Some applications it can be used with:
    1. Firefox
    2. Thunderbird
    3. Chromium
    4. OpenSSH
    5. OpenConnect (VPN)
    6. Kerberos
    7. PAM (pam_pkcs11 module can load pkcs11 modules)

Loading the module will differ for each application.  Here's how you do it
in current versions of Firefox on Linux:
    https://developer.mozilla.org/en-US/docs/Mozilla/Projects/NSS/PKCS11/Module_Installation

Chromium on Linux:
    https://help.ubuntu.com/community/CommonAccessCard#Google_Chrome.2FChromium_Setup

OpenSSH is done by using either "ssh -I <module>" or (better) using an SSH
agent, for OpenSSH that would be done by using "ssh-add -s <module>".

OpenConnect is more complicated since it uses ilbp11.

Kerberos is done using PKINIT with a PKCS11 provider:
    https://k5wiki.kerberos.org/wiki/Pkinit_configuration
    http://web.mit.edu/Kerberos/krb5-1.9/krb5-1.9.1/doc/krb5-admin.html#pkinit-client-options

The pam_pkcs11 configuration is similarly complex, but targeted at PKCS#11.