This lab involves a front-end and back-end server, and the front-end server doesn't support chunked encoding. The front-end server is caching static resources.
To solve the lab, perform a request smuggling attack such that the next user's request causes their API key to be saved in the cache. Then retrieve the victim user's API key from the cache and submit it as the lab solution.
You have an account on the application that you can use to help design your attack. The credentials are: carlos / montoya.
The lab simulates the activity of a victim user. Every few POST requests that you make to the lab, the victim user will make their own request. You might need to repeat your attack a few times to ensure that the victim user's request occurs as required.
Log in to your account.
Click "API Key" on the top right, and observe that the response doesn't have any anti-caching headers.
Smuggle a request to fetch the API key:
POST / HTTP/1.1
GET /apiKey HTTP/1.1
Repeat this request a few times, then load the home page in an incognito browser window.
Use the Search function on the Burp menu to see if the phrase "Your API Key" has appeared in any static resources. If it hasn't, repeat the POST requests, force-reload the browser window, and re-run the search.
Submit the victim's API key as the lab solution.