Install proxy certificate

At my work a SSL proxy certificate has to be installed in order to have internet access.
How can I do this on HA?

I got the company .p12 file (with a password) and I was able to convert it to a .pem or .crt file (if even needed)

But what to do now so HA can access internet for updates and addons?
Searching for it gives me mostly results to access HA itself on https but that’s not wat I want. Just a certificate to gain internet access via our network.