So the first port vs. alternate port behavior for HTTP_PORT is documented here: https://docs.sandstorm.io/en/latest/administering/config-file/ and HTTP_PORT can be specified as a comma-separated list. However, HTTPS_PORT is specified as a single port, and specifies that the HTTPS_PORT will be treated as the first port if enabled. However, there is no support for HTTPS alternate ports.

The problem is that since Oasis shut down, I have operated my Sandcats server on a nonstandard port (6080, but using HTTPS), because my ISP had an explicit terms of use prohibiting exposing any server software on a well-known port (such as 443). However, that ISP recently sold my geographic area to another ISP with different terms which do not prohibit using well-known ports. Moving my server would solve a lot of problems, like letting me host websites cached via Cloudflare (and other external services which expect normal ports for things). However, that would break all of my existing HTTPS sharing links and API keys out in the world, which would be very sad and frustrating.