Generate Client cert and pem without subscription manager

Is there a way to manually generate and assign a sslclientcert and key for manual configuration on a system.
Expected outcome:
a system that is able to access repositories hosted by The Foreman, but not necessarily use subscription-manager
Foreman and Proxy versions:
Foreman and Proxy plugin versions:
Other relevant data:
this might just be a generic question. But say I have a client that doesn’t support any distribution of subscription manager and say my foreman environment requires the use of https for connectivity from clients to proxies or the foreman server itselft.

Can I manually (or through process) generate a client cert and key and then use that on a client to access given repositories?