Good day. The essence of the problem: The old version of some software works only on HTTP. A more modern version of the same software can only HTTPS. Immediately disable the old hundreds of users fail. You need something like a mini-server that can receive requests to itself on port 80 and send it to an external resource on port 443, followed by a dialogue, of course. stunnel, as I understand it, does not know how. NGINX and Apache make a simple redirect with URL substitution. Proxy servers? But which one? Or create it yourself? - then what? I met non-working examples on Node.js and python.
Anyway, thanks.