Once again, I don't have a full answer, but some experience to relate.
With the whole world (seemingly) migrating to https: from http:, I decided to give that a try.
My setup is as follows: (using generic domain and page names, not the real ones)
mydomain.com is where people access the front end of the application,
and then JS code there connects to another server, which is where Union runs.
So, I got a certificate installed (thanks to my webhost) and opened
https://mydomain.com/unionapppage.htmlThat part worked fine, as does most of the website which doesn't try to talk to Union.
The connection to Union didn't work at all (using the normal websocket connect code).
Probably what is needed is to get a certificate installed on the Union server side of things,
and use a secure connection to it. The instructions for doing that are a bit complicated,
and I did not really try to do it.
That possibility probably doesn't exist for
tryunion.com, but I don't know for sure.