Sign container images

Author: David Collom

.github/workflows/release.yaml

@@ -6,6 +6,8 @@ on:
       - "release-v*"
     tags:
       - "v*"
+  # TODO: Added for testing....
+  workflow_dispatch:
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}
@@ -153,6 +155,14 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
+
+      # Install the cosign tool except on PR
+      # https://github.com/sigstore/cosign-installer
+      - name: Install cosign
+        uses: sigstore/cosign-installer@59acb6260d9c0ba8f4a2f9d9b48431a222b68e20 #v3.5.0
+        with:
+          cosign-release: "v2.2.4"
+
       - name: Set up QEMU
         uses: docker/setup-qemu-action@v3
 
@@ -169,6 +179,7 @@ jobs:
           password: ${{ secrets.QUAY_ROBOT_TOKEN }}
 
       - name: Build and push (if applicable)
+        id: build-and-push
         uses: docker/build-push-action@v6
         with:
           context: .
@@ -179,6 +190,21 @@ jobs:
           cache-from: type=gha
           cache-to: type=gha,mode=max
 
+      # Sign the resulting Docker image digest except on PRs.
+      # This will only write to the public Rekor transparency log when the Docker
+      # repository is public to avoid leaking data.  If you would like to publish
+      # transparency data even for private images, pass --force to cosign below.
+      # https://github.com/sigstore/cosign
+      - name: Sign the published Docker image
+        if: ${{ startsWith(github.ref, 'refs/tags/') }}
+        env:
+          # https://docs.github.com/en/actions/security-guides/security-hardening-for-github-actions#using-an-intermediate-environment-variable
+          TAGS: ${{ steps.meta.outputs.tags }}
+          DIGEST: ${{ steps.build-and-push.outputs.digest }}
+        # This step uses the identity token to provision an ephemeral certificate
+        # against the sigstore community Fulcio instance.
+        run: echo "${TAGS}" | xargs -I {} cosign sign --yes {}@${DIGEST}
+
   github-release:
     name: Create/Update GitHub Release
     permissions: