This website has an unauthenticated admin panel at /admin, but a front-end system has been configured to block external access to that path. However, the back-end application is built on a framework that supports the X-Original-URL header.
To solve the lab, access the admin panel and delete the user carlos.
Try to load /admin and observe that you get blocked.
Observe that the response is very plain, suggesting it may originate from a front-end system.
Send the request to Burp Repeater. Change the URL in the request line to / and add the HTTP header X-Original-URL: /invalid. Observe that the application returns a "not found" response. This indicates that the back-end system is processing the URL from the X-Original-URL header.
Change the value of the X-Original-URL header to /admin. Observe that you can now access the admin page.
To delete the user carlos, add ?username=carlos to the real query string, and change the X-Original-URL path to /admin/delete.