Pass file secrets to "podman build" via parameter "--secret"

[wiehe]

Dear maintainers!

At the moment podman-compose always passes file secrets to podman as a --volume option, both when starting containers and when building images.
I propose that file secrets for building are instead passed as a --secret option. This would make them available for
RUN --mount=type=secret… instructions and would improve compatibility with docker-compose.

Example

# Dockerfile
FROM busybox
RUN --mount=type=secret,required=true,id=my_secret,target=/root/my_secret \
		echo "The secret is: "; cat /root/my_secret

To build directly from this Dockerfile one has to supply the secret like this:
podman build --secret=id=my_secret,src=./my_secret .

# docker-compose.yaml
services:
  my-service:
    build:
      context: .
      secrets:
        - my_secret

secrets:
  my_secret:
    file: ./my_secret

Building from the docker-compose.yaml with podman-compose build my-service should produce the same results as the podman build … command above.

Yours sincerely
wiehe

[p12tic]

Thanks for the PR. It looks good.

Please rebase on top of latest main branch and add unit tests (see pytest/ directory for examples).

[wiehe]

Hi, thanks for considering my pull request! I have rebased it onto main and ported the test script from pytest to unittest.