How to have domain-mapped containers use existing server ssl cert for the domain

So I’ve been having an unnatural amount of fun creating a server running a web hosting panel for my sites, and then adding sefl hosted apps with docker. The main domain loads over port 443 on https protocol using a letsencrypt ssl cert gererated by the webhosting control panel. The panel is not running in a docker container. I get a shiny padlock in my browser when I visit

For the self hosted apps in containers, I’ve mapped the internal ports to available external ports and opened those ports on the server firewall. When I visit I get NET::ERR_CERT_AUTHORITY_INVALID

I think my problem is that the containers were launched using
-p my-ip-address:external-port:container-port
and I should have specified a domain name instead, but I’m not sure if the containers can piggyback on the external server ssl, and even if they can I don’t know what the syntax might be.