I fail to see why the ssl configuration has to do with the apps behind the proxy 
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as long as the ssl template is disable in the app.yml ? nginx or apache or haproxy or traefik, they all have the same snippet/serverblock/virtualhost concept where basically you specify ssl on, then where your certificates are located on your host and a few ssl parameters, here be dragons maybe?
I think the solution you are looking for in not discourse related but apache related, and I believe that any out off the box working ssl apache config with virtual host will work fine with discourse, as it has worked with others reverse proxies, but I might be a bit optimistic 
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Though I remember having an issue with the ciphers maybe, you want to be sure to copy/paste carefully (the line is very long) those in use within the docker container.
About this slippery slope, i think it’s kind of skiing off-track, it’s great but it’s very frowned upon by the mountain rescue, and I admit reasonably differently when you fall in a ravine while still learning whether being an accomplish skier.
Please, professional or not, be kind to the
