Merge pull request #40 from anderbubble/fix-cosign

Update container signing action from upstream example

.github/workflows/container-publish.yml

@@ -87,9 +87,8 @@ jobs:
       - name: Checkout repository
         uses: actions/checkout@v3
 
-      # Install the cosign tool except on PR
+      # Install the cosign tool
       # https://github.com/sigstore/cosign-installer
-
       - name: Install Cosign
         if: github.event_name != 'pull_request'
         uses: sigstore/[email protected]
@@ -98,7 +97,7 @@ jobs:
       - name: Setup Docker buildx
         uses: docker/setup-buildx-action@f03ac48505955848960e80bbb68046aa35c7b9e7
 
-      # Login against a Docker registry except on PR
+      # Login against a Docker registry
       # https://github.com/docker/login-action
       - name: Log into registry ghcr.io
         if: github.event_name != 'pull_request'
@@ -121,7 +120,7 @@ jobs:
             type=schedule
             type=raw,${{ matrix.version }}
 
-      # Build and push Docker image with Buildx (don't push on PR)
+      # Build and push Docker image with Buildx
       # https://github.com/docker/build-push-action
       - name: Build and push image
         id: build-and-push
@@ -136,16 +135,20 @@ jobs:
           cache-from: type=gha
           cache-to: type=gha,mode=max
 
+      # https://docs.github.com/en/actions/security-guides/security-hardening-for-github-actions#using-an-intermediate-environment-variable
+      - name: Sign image with a key
+        if: github.event_name != 'pull_request'
+        run: |
+          cosign sign --yes --key env://COSIGN_PRIVATE_KEY "${TAGS}@${DIGEST}"
+        env:
+          TAGS: ${{ steps.docker_meta.outputs.tags }}
+          COSIGN_PRIVATE_KEY: ${{ secrets.COSIGN_PRIVATE_KEY }}
+          COSIGN_PASSWORD: ${{ secrets.COSIGN_PASSWORD }}
+          DIGEST: ${{ steps.build-and-push.outputs.digest }}
 
-      # Sign the resulting 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 image
-        if: ${{ github.event_name != 'pull_request' }}
+      - name: Sign the images with GitHub OIDC Token
+        if: github.event_name != 'pull_request'
         env:
-          COSIGN_EXPERIMENTAL: "true"
-        # This step uses the identity token to provision an ephemeral certificate
-        # against the sigstore community Fulcio instance.
-        run: echo "${{ steps.meta.outputs.tags }}" | xargs -I {} cosign sign --yes {}@${{ steps.build-and-push.outputs.digest }}
+          DIGEST: ${{ steps.build-and-push.outputs.digest }}
+          TAGS: ${{ steps.docker_meta.outputs.tags }}
+        run: cosign sign --yes "${TAGS}@${DIGEST}"