esnextb.in is getting CORS error on POST ./multi

```
Access to XMLHttpRequest at 'https://wzrd.in/multi' from origin 'https://esnextb.in' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource.
```
https://esnextb.in

Start by reproducing the POST request to https://wzrd.in/multi from https://esnextb.in and inspect the server entry point handling /multi and its preflight response. Done means the preflight and POST responses include the required CORS headers so the request is accepted from esnextb.in.

Written by the indexing model from the issue text.