Currently, Docker Runner only connects to public Docker Image Registries to pull images from, such as hub.docker.com
Please add the capability to connect to private registries to pull images.
Allow auth to private registries through input credentials, or the Shared Credentials
Add the docker login command to the .profile of the Remote Agent user, for each Agent which will be using the Docker Runner build capability.
To keep from having passwords stored in plain text in a script you can use the credential helper as outlined in the documentation for docker login