Redirects to HTTP when behind HTTPS reverse proxy

[dnrce]

When terminating TLS on a reverse proxy in front of script-server, any redirects returned by script-server should use the HTTPS scheme, but the current behavior is that they use HTTP regardless. https://github.com/bugy/script-server/wiki/Reverse-Proxy-setup says to set the X-Scheme header in this scenario, but it is not respected.

Here's a docker-compose.yml to reproduce the issue:

---
version: '3.1'

services:

  script-server:
    image: bugy/script-server:dev

  reverse-proxy:
    image: caddy:2.3.0
    command:
      - sh
      - -c
      - |
        echo -e 'localhost

        reverse_proxy script-server:5000 {
          header_up X-Scheme {scheme}
        }' | caddy run --adapter caddyfile --config -
    ports:
      - 127.0.0.1:443:443

When querying via HTTPS, script-server issues a redirect back to HTTP:

$ curl -k -v https://localhost 2>&1 | grep -i location:
< location: http://localhost/index.html

(It's also worth noting that X-Scheme is a nonstandard header. X-Forwarded-Proto is the more de-facto standard and the proto directive of the Forwarded header is an actual standard.)

[bugy]

Done. I tested it for tornado5 and tornado6, seems to be working.
Now X-Scheme and X-Forwarded-Proto headers are always respected, but no other x-headers

Thanks for the docker compose, was really helpful!