Comment # 8 on bug 1233373 from M Fredericks

After booting without “splash=silent quiet” I did run

> systemctl start systemd-ask-password-console.service

And that give window popping up asking for a Password and if I give the root
password it disappears. If I give another password it fails ans asks again and
if I wait too long it times out.

> systemd-tty-ask-password-agent --help
systemd-tty-ask-password-agent [OPTIONS...]

Process system password requests.

  -h --help              Show this help
     --version           Show package version
     --list              Show pending password requests
     --query             Process pending password requests
     --watch             Continuously process password requests
     --wall              Continuously forward password requests to wall
     --plymouth          Ask question with Plymouth instead of on TTY
     --console[=DEVICE]  Ask question on /dev/console (or DEVICE if specified)
                         instead of the current TTY

So I am not too surprised about --watch (without knowing what it is doing
exactly) but I hope it is started during boot using --plymouth although
"systemctl cat systemd-ask-password-console.service" does not show that.