Some have asked me to reboot the addon for 2.x. If you'd like to see this add-on updated please leave a comment here: https://xenforo.com/community/threads/rebooting-custom-markup-for-user-add-on.178673/
A few years ago I made the original Custom Markup for User add-on. @DarkGizmo has PM'd me asking if I would upgrade the add-on for 2.x.
I was wondering if there's any interest for this add-on still? (In 2020 I think they're rather tacky.) Maybe @IGN Engineering ?
This is pretty much saying "Knowing how to put legos together will get you a lego tower", but yes. XenForo is written in PHP.
You'll also need to know the basics of database administration to interact with the database, and HTML/CSS/JS to write front-end code.
Apologies, I removed my last post because I realised I misunderstood your post.
If your WAF can look up XF's datastore then you should be able to look up user info with the `xf_session` cookie, which contains the session ID. How much of a performance penalty I don't know - depends on where you...