The problem: osbuild-composer used to have a rather uncomplete logic for
selecting client certificates and keys while fetching data from
repositories that use the "subscription model". In this scenario, every
repo requires the user to use a client-side TLS certificate. The problem
is that every repo can use its own CA and require a different pair of
a certificate and a key. This case wasn't handled at all in composer.
Furthermore, osbuild-composer can use remote workers which complicates
things even more.
Assumptions: The problem outlined above is hard to solve in the general
case, but Red Hat Subscription Manager places certain limitations on how
subscriptions might be used. For example, a subscription must be tight to
a host system, so there is no way to use such a repository in osbuild-composer
without it being available on the host system as well.
Also, if a user wishes to use a certain repository in osbuild-composer it
must be available on both hosts: the composer and the worker. It will come
with different pair of a client certificate and a key but otherwise, its
configuration remains the same.
The solution: Expect all the subscriptions to be registered in the
/etc/yum.repos.d/redhat.repo file. Read the mapping of URLs to certificates
and keys from there and use it. Don't change the manifest format and let
osbuild guess the appropriate subscription to use.