Multi-Vendor Survey Redirect Layer

I’m managing an online survey in which the client has already embedded three exit links—India-Complete, India-Quota Full, and India-Terminate. Two external sample vendors will drive respondents to the study, and each vendor will supply its own entry and finish URLs. I need a compact redirect layer that sits between the vendors and the client survey so respondents are invisibly routed to the correct vendor-specific finish link while the client links remain hidden.

How the flow should work
• Each vendor lands on a dedicated URL you create, making it clear which vendor the respondent belongs to. This vendor-specific landing page then passes the user straight into the client survey, preserving every query-string parameter the vendor attaches.
• When the client survey fires one of the three India links, your script must read the status code (Complete, Quota Full, Terminate) and conditionally route the respondent back to the matching finish link for the originating vendor—never to the wrong one and never exposing the client URL.

Key requirements
• Conditional redirect based solely on vendor (no round-robin or random routing)
• Vendor identification handled through separate landing pages rather than a shared parameter
• Status tracking via the standard codes Complete / Quota Full / Terminate
• Full parameter passthrough and <200 ms response time so respondents don’t notice the hop
• Solution delivered as a lightweight script (PHP, Node, Cloudflare Worker, etc.) plus concise setup notes so I can host and test it myself

Acceptance criteria
1. Vendor A and Vendor B traffic both reach the client survey without loss.
2. Completes, quota fulls, and terminates are returned to the correct vendor-specific URLs every time.
3. The client’s links never appear in the browser or network logs.
4. Documentation shows me how to add another vendor later.

If you’ve built similar redirect or traffic-management layers for online surveys, please share one example so I can gauge fit.