Thanks for your answer phoenix!
Didn't work though.. I wiped my installation and reinstalled 5.0.6 using the proxy-setting. Then I tried zmtlsctl with http, https, both, mixed.
Mixed doesn't work (as the instructions say),
https doesn't work either (502 Bad Gateway both on http and https),
http obviously doesn't do what I want but not what I expect either. I get a login page even on https but when logging in it redirects me to http. The same thing with
both, redirection from https to http.
I'm really stumped here, especially that http gives a login page on https.. And mostly that https won't keep me in https!

Or have I misunderstood the proxying or the combitaion with zmtlsctl? Any other tips?
/K