This is useful in PolicyKit applications running in a non-graphical environment. It's simple to use: simply use PolkitAgentTextListener if the response from PolicyKit indicates that authorization can be obtained if more information is provided. Here are the changes that was needed for pkexec(1) command. An obvious candidate for this would be the pkcon(1) command.
For authentication, the Shell is using the existing code that in turn uses PAM. This means that the Authorization Dialog will work out-of-the-box with e.g. fingerprint readers, provided, of course, that the PAM stack has been set up correctly (video).
Additionally, the code has been tested with pam_rps - a PAM module whereby you authenticate by proving that you are smart enough to win in Rock-paper-scissors. The idea is that if your application works with pam_rps, then there's a good chance that it will work with any PAM module (video).
One major difference - and something I've been wanting to do for a while - is that the dialogs are now system-modal. In addition to fixing a lot of focus problems, this also makes the dialogs look more trustworthy since they are part of the actual shell. They're also way prettier.
(Bonus chatter: Of course, there's an emphasis on look in the above paragraph because any random app can still go full-screen to fool the user to give them their password. To do this in a more secure way, we need to use the Secure Attention Key and run the dialog in another security context etc. It's an open question whether it's even worth it to do this. But I digress.)
You can find the current code drop in this bug.
