hello, as for me, i’ve configured nexus to proxy this url
https://cdn.redhat.com/content/dist/rhel/server/7/7Server/x86_64
and client side is like this:
###RH7 Repo###
[rh7-proxy-devtools]
name=RH7 Proxy Devtools
baseurl=http://repo.sitename.ru:8081/repository/rh7-proxy/devtools/1/os
enabled=1
gpgcheck=1
gpgkey=http://repo.sitename.ru:8081/repository/KEYS/rpm/RPM-GPG-KEY-redhat-release
So for extras/os this looks like
[rh7-proxy-extras]
name=RH7 Proxy extras
baseurl=http://repo.sitename.ru:8081/repository/rh7-proxy/extras/os
enabled=1
gpgcheck=1
gpgkey=http://repo.sitename.ru:8081/repository/KEYS/rpm/RPM-GPG-KEY-redhat-release
hope that will help