private key local authentication
 

I've googled a bit and i've only found people talking about pub/private keys to authenticate for ssh, but what about local authentication?

I anticipate that the first question is going to be 'why?'
Well, i just want to see if I can actually get it to work.

but the idea is that any time i need my user password, i authenticate with a key, not typing a password.

The key has to be invoked by some action.

I use disk encryption (LUKS) and am the only one who uses my machine, so I have KDE set to auto-login. I give the password on boot for / and swap, then it comes right up.