Really having trouble finding anything outside of oauth workflows.

Captive recipients should authenticate via an ISV app. This video talks about it: https://www.youtube.com/watch?v=0wdWMIXE9l8 however there's no matching documentation I could find other than https://developers.docusign.com/docs/esign-soap-api/esign101/embedding/captive-recipients/ which doesn't give an explanation on how to actually use it.