Unless you're at Google (or writing your own backend), jj talks to a git server, and so you'd just do exactly that: host a git repo over https.
[1] https://pkg.go.dev/github.com/shurcooL/home/internal/code#Ne...
[2] https://pkg.go.dev/github.com/shurcooL/home/cmd/githook/pre-...
You should be able to use jj with your server just fine.