Environment:
Centos 7, all updates as of 2018-10-19
Foreman 1.19, all updates as of 2018-10-19

Problem:

foreman-installer does not provide the ability to choose custom certs when installing foreman ONLY for the httpd:

[root@foreman-d-01 httpd]# foreman-installer --help|grep -i certs-server
[root@foreman-d-01 httpd]#

In an installation with scenario katello there is the ability:
[root@katello4 foreman-installer]# foreman-installer --help|grep -i certs-server
--certs-server-ca-cert Path to the CA that issued the ssl certificates for https
--certs-server-cert Path to the ssl certificate for https
--certs-server-cert-req Path to the ssl certificate request for https
--certs-server-key Path to the ssl key for https

Steps to reproduce:
1.) Install foreman (without katello)
2.) Run foreman-installer (without parameters)
3.) Run foreman-installert --help|grep certs-server