[DOCKER] Sign multi-arch image

[Renizmy]

Hello !

Based on this circle-ci step:

    steps:
      - checkout
      - setup_remote_docker
      - run:
          name: Build renizmy/python-client-container <<parameters.python_version>> <<parameters.tag>>
          command: |
            docker run --privileged --rm tonistiigi/binfmt --install linux/amd64,linux/arm64
            CIRCLE_TAG=${CIRCLE_TAG:-latest}
            docker buildx create --platform linux/amd64,linux/arm64 --use --name mybuilder 
            docker buildx inspect mybuilder --bootstrap
            echo "$DOCKERHUB_PASS" | docker login -u "$DOCKERHUB_USERNAME" --password-stdin
            docker buildx build . \
              --platform linux/amd64,linux/arm64 \
              -t <<parameters.base_repo>>/client-python-<<parameters.python_version>>:${CIRCLE_TAG} \
              -t <<parameters.base_repo>>/client-python-<<parameters.python_version>>:latest \
              --build-arg BASE_IMAGE="<<parameters.base_image>>" \
              --cache-to=type=local,dest=client-python-<<parameters.python_version>>.tmp \
              --push

I'm trying to determine the proper output format for the docker buildx build command to sign a multi-arch image (including each sub-image) using cosign. However, it doesn't seem to work with each output (oci, tar, ..)

docker buildx build documentation: https://docs.docker.com/reference/cli/docker/buildx/build/#output

Does anyone have any suggestions?

Best regards,