This plugin will not log in when a slave agent goes down and another one replaces it. You must manually bash into the agent and run "docker login" to get it to work again.
Upon further testing, it looks like registry auth is not working at all:
docker-commons 1.3.1 (required for "sha256" prefix required in new version of docker)
Attempts to publish get:
unauthorized: authentication required
If you run docker login manually from bash and the credentials get stored in .docker/config.json then it will start working, but I will not login on it's own. I've confirmed that the username and password we have set in credentials is correct.