Setup Foreman + Katello with valid Certificates

Problem:
The instructions for replacing the certificate on this site:
https://theforeman.org/2015/11/foreman-ssl.html
are quite outdated (e.g. the paths have changed), furthermore there are always problems with the smart proxy (e.g. when the smart proxy sends data back, it says, that the certificates don’t match (even if it is running on the same system)).

Expected outcome:
A valid certificate in the foreman frontend (important especially for chrome users) and full functionality for the foreman smart-proxies

Foreman and Proxy versions:

1.13.*
(didn’t check more versions)

Foreman and Proxy plugin versions:

1.13.*
(didn’t check more versions)

I have a type here:
It’s:

1.13.*