Support for docker secrets

[Vampire]

It would be great if the docker image would support docker secrets, so that things like GitHub credentials can be safely stored without building them into the image or providing them through environment variables.

[paulmelnikow]

Hi! Thanks for the suggestion. Would be great to support this. Do you know what's involved? Would you be interested in working on it?

[Vampire]

You can find more information at https://docs.docker.com/engine/swarm/secrets/ and especially https://docs.docker.com/engine/swarm/secrets/#build-support-for-docker-secrets-into-your-images.

Basically you just have to support configuring files from which confidential information is read instead of configuring the confidential data themselves.

[paulmelnikow]

Some relevant discussion / implementation in #2621 and #2626. These don't address docker secrets directly, though we could implement those with docker secrets in mind.