Add tracking script to challenge page to track original document.referrer

[robbie4]

What is the name of the domain?

Example Domain

What is the issue you’re encountering

I want to add a tracking script to a challenge page so that I can track the original document.referrer

What steps have you taken to resolve the issue?

According to the docs here Challenges · Cloudflare Fundamentals docs I need to add a tracking script to the challenge page to be able to track the original referrer. How can I do this? I can see how to customize error pages here Custom Errors · Cloudflare Rules docs but not challenge pages.