@andydavies: Thanks a bunch for your help on this.
Unfortunately I am a proxy guy and this is for a prospect of mine. I can ask them but its gonna take a while and strongly prefer if there is a way we can automate the login via WPT.
I’ll be looking at the scripting support a bit next week, but if all else fails, exec and execAndWait are your friends. You can use javascript to manipulate the form and you can debug it locally in your dev tools to make sure it works before submitting it.