While I’m sure there’s a pre-canned tool out there for you, if you have basic software experience (which you seem to), this is one of those times where it’s usually most efficient to hack together a dumb CGI script and call it a day.
This prompt should get you most of the way there, using your llm of choice:
Write a minimalist cgi script to help upload files to a server. Upon a GET request, serve a light page with a centered form that takes in a file and a submission code. Submission codes will be stored on individual lines of a plaintext file. Adding new codes to this file is out of scope - but the codes will be 8-char hex strings (do validate that submission strings are not empty!). The script should accept the submission as a POST, and save the file to an upload dir if the submission code is valid.
Vet the output, harden as needed, setup a systemd service to serve with busybox httpd, and optionally reverse-proxy. If you’ve done this sorta thing before, you can probably knock it out in a half hour.
Not a triad user in sight.
Just lemmings living in the moment.