Thanks! The "Login" button now opens up Firefox and I can complete my login there w/ my Yubikey!

BZ#2107412 OpenConnect cannot open browser to complete SAML auth

Things seem to be working as expected. I verified that a few different USB devices plus an onboard Intel device worked on hardware.

The steps in "pavucontrol add remove" don't seem to quite work as expected since my PC doesn't seem to have jack sensing support working. Honestly I have never used the onboard audio so there is a chance that it might be too old. If I set a USB device to default, then unplug it, playback continues on another device. If I plug the original back in it's shown in pavucontrol as default again.