I was using secretEnv previously to pass in credentials for my docker repository as environment vars from a K8S secret in a scripted syntax job. This was working before the most recent plugin update and I just used the ENV in a docker login script. Originally I wanted to use the image-pull-secret to just mount a config.json file at /root/.docker/config.json but that also didn't work as I think the plugin doesn't know how to mount a kubernetes.io/dockerconfigjson type. My final attempt was to pass the host volume at /root/.docker into the guest which also didn't work. I imagine others will want to pass the host docker config in since they are already using the docker.sock socket. 

hostPathVolume(hostPath: '/root/.docker', mountPath: '/root/.docker')