Support building Dockerfiles that mount secrets as environment variables

[carles-garcia]

Feature request description

Since Dockerfile 1.10 the Docker Engine can mount secrets as environment variables specified in the RUN command.

https://docs.docker.com/build/buildkit/dockerfile-release-notes/#1100

https://docs.docker.com/reference/dockerfile/#example-mount-as-environment-variable

It would be useful for podman build to support it. It's already possible using podman run.

[rhatdan]

@flouthoc any chance you could look at this?

[flouthoc]

I'll take a look at this.

[github-actions]

A friendly reminder that this issue had no activity for 30 days.

[hdub-tech]

This works in podman and buildah. I recently submitted a PR to update the podman build documentation Examples to demonstrate how to use podman build with secrets in environment variables, and I am planning to submit a similar one for the buildah documentation. There is already an example on Issue #5808, with the clarification that it was just using the wrong case in the id field of the buildah command.