Building of container images using Buildah as a non-root user

$ oc get task buildah -n openshift-pipelines -o yaml | yq '. |= (del .metadata |= with_entries(select(.key == "name" )))' | yq '.kind="Task"' | yq '.metadata.name="buildah-as-user"' | oc create -f -

$ oc edit task buildah-as-user

apiVersion: tekton.dev/v1
kind: Task
metadata:
  name: buildah-as-user
spec:
  description: >-
    Buildah task builds source into a container image and
    then pushes it to a container registry.
    Buildah Task builds source into a container image using Project Atomic's
    Buildah build tool.It uses Buildah's support for building from Dockerfiles,
    using its buildah bud command.This command executes the directives in the
    Dockerfile to assemble a container image, then pushes that image to a
    container registry.
  params:
  - name: IMAGE
    description: Reference of the image buildah will produce.
  - name: BUILDER_IMAGE
    description: The location of the buildah builder image.
    default: registry.redhat.io/rhel8/buildah@sha256:99cae35f40c7ec050fed3765b2b27e0b8bbea2aa2da7c16408e2ca13c60ff8ee
  - name: STORAGE_DRIVER
    description: Set buildah storage driver
    default: vfs
  - name: DOCKERFILE
    description: Path to the Dockerfile to build.
    default: ./Dockerfile
  - name: CONTEXT
    description: Path to the directory to use as context.
    default: .
  - name: TLSVERIFY
    description: Verify the TLS on the registry endpoint (for push/pull to a non-TLS registry)
    default: "true"
  - name: FORMAT
    description: The format of the built container, oci or docker
    default: "oci"
  - name: BUILD_EXTRA_ARGS
    description: Extra parameters passed for the build command when building images.
    default: ""
  - description: Extra parameters passed for the push command when pushing images.
    name: PUSH_EXTRA_ARGS
    type: string
    default: ""
  - description: Skip pushing the built image
    name: SKIP_PUSH
    type: string
    default: "false"
  results:
  - description: Digest of the image just built.
    name: IMAGE_DIGEST
    type: string
  workspaces:
  - name: source
  steps:
  - name: build
    securityContext:
      runAsUser: 1000 (1)
    image: $(params.BUILDER_IMAGE)
    workingDir: $(workspaces.source.path)
    script: |
      echo "Running as USER ID `id`" (2)
      buildah --storage-driver=$(params.STORAGE_DRIVER) bud \
        $(params.BUILD_EXTRA_ARGS) --format=$(params.FORMAT) \
        --tls-verify=$(params.TLSVERIFY) --no-cache \
        -f $(params.DOCKERFILE) -t $(params.IMAGE) $(params.CONTEXT)
      [[ "$(params.SKIP_PUSH)" == "true" ]] && echo "Push skipped" && exit 0
      buildah --storage-driver=$(params.STORAGE_DRIVER) push \
        $(params.PUSH_EXTRA_ARGS) --tls-verify=$(params.TLSVERIFY) \
        --digestfile $(workspaces.source.path)/image-digest $(params.IMAGE) \
        docker://$(params.IMAGE)
      cat $(workspaces.source.path)/image-digest | tee /tekton/results/IMAGE_DIGEST
    volumeMounts:
    - name: varlibcontainers
      mountPath: /home/build/.local/share/containers (3)
  volumes:
  - name: varlibcontainers
    emptyDir: {}

apiVersion: v1
data:
  Dockerfile: |
    ARG BASE_IMG=registry.access.redhat.com/ubi9/ubi
    FROM $BASE_IMG AS buildah-runner
    RUN dnf -y update && \
        dnf -y install git && \
        dnf clean all
    CMD git
kind: configmap
metadata:
  name: dockerfile (1)
---
apiVersion: tekton.dev/v1
kind: TaskRun
metadata:
  name: buildah-as-user-1000
spec:
  taskRunTemplate:
    serviceAccountName: pipelines-sa-userid-1000 (2)
  params:
  - name: IMAGE
    value: image-registry.openshift-image-registry.svc:5000/test/buildahuser
  taskRef:
    kind: Task
    name: buildah-as-user
  workspaces:
  - configmap:
      name: dockerfile (3)
    name: source

apiVersion: tekton.dev/v1
kind: Pipeline
metadata:
  name: pipeline-buildah-as-user-1000
spec:
  params:
  - name: IMAGE
  - name: URL
  workspaces:
  - name: shared-workspace
  - name: sslcertdir
    optional: true
  tasks:
  - name: fetch-repository (1)
    taskRef:
      resolver: cluster
      params:
      - name: kind
        value: task
      - name: name
        value: git-clone
      - name: namespace
        value: openshift-pipelines
    workspaces:
    - name: output
      workspace: shared-workspace
    params:
    - name: URL
      value: $(params.URL)
    - name: SUBDIRECTORY
      value: ""
    - name: DELETE_EXISTING
      value: "true"
  - name: buildah
    taskRef:
      name: buildah-as-user (2)
    runAfter:
    - fetch-repository
    workspaces:
    - name: source
      workspace: shared-workspace
    - name: sslcertdir
      workspace: sslcertdir
    params:
    - name: IMAGE
      value: $(params.IMAGE)
---
apiVersion: tekton.dev/v1
kind: PipelineRun
metadata:
  name: pipelinerun-buildah-as-user-1000
spec:
  taskRunSpecs:
    - pipelineTaskName: buildah
      taskServiceAccountName: pipelines-sa-userid-1000 (3)
  params:
  - name: URL
    value: https://github.com/openshift/pipelines-vote-api
  - name: IMAGE
    value: image-registry.openshift-image-registry.svc:5000/test/buildahuser
  pipelineRef:
    name: pipeline-buildah-as-user-1000
  workspaces:
  - name: shared-workspace (4)
    volumeClaimTemplate:
      spec:
        accessModes:
          - ReadWriteOnce
        resources:
          requests:
            storage: 100Mi