Cosign artifacts (closes #1039)

.github/workflows/ci.yml

@@ -41,6 +41,8 @@ jobs:
     needs: [linux]
     if: github.event_name == 'push' || inputs.Docker
     steps:
+      - name: Install Cosign
+        uses: sigstore/cosign-installer@v3
       - name: Log In to GitHub Container Registry
         uses: docker/login-action@v3
         with:
@@ -82,6 +84,8 @@ jobs:
           echo "GHCR_DIGEST_SHA=$(cat GHCR_DIGEST_SHA)" | tee -a "${GITHUB_ENV}"
           docker buildx imagetools inspect --format '{{json .Manifest}}' index.docker.io/${{github.repository}}:$(jq -r '.target."docker-metadata-action".args.DOCKER_META_VERSION' ${{ runner.temp }}/${{matrix.variant}}/bake-meta.json) | jq -r '.digest' > DOCKERHUB_DIGEST_SHA
           echo "DOCKERHUB_DIGEST_SHA=$(cat DOCKERHUB_DIGEST_SHA)" | tee -a "${GITHUB_ENV}"
+          cosign sign --yes $(jq --arg GHCR_DIGEST_SHA "$(cat GHCR_DIGEST_SHA)" -cr '.target."docker-metadata-action".tags | map(select(startswith("ghcr.io/${{github.repository}}")) | . + "@" + $GHCR_DIGEST_SHA) | join(" ")' ${{ runner.temp }}/${{matrix.variant}}/bake-meta.json)
+          cosign sign --yes $(jq --arg DOCKERHUB_DIGEST_SHA "$(cat DOCKERHUB_DIGEST_SHA)" -cr '.target."docker-metadata-action".tags | map(select(startswith("index.docker.io/${{github.repository}}")) | . + "@" + $DOCKERHUB_DIGEST_SHA) | join(" ")' ${{ runner.temp }}/${{matrix.variant}}/bake-meta.json)
 
       - name: Attest GHCR
         uses: actions/attest-build-provenance@v2
@@ -411,16 +415,25 @@ jobs:
             archive/**/*.tar.gz
             archive/**/*.zip
 
+      - name: Use cosign to sign existing artifacts
+        uses: sigstore/gh-action-sigstore-python@v3.0.0
+        with:
+          inputs: |
+            archive/**/*.tar.gz
+            archive/**/*.zip
+
       - name: Release
         uses: softprops/action-gh-release@v2
         with:
           files: |
             archive/**/*.tar.gz
             archive/**/*.zip
+            archive/**/*.sigstore.json
           prerelease: ${{!startsWith(github.ref, 'refs/tags/') || null}}
           tag_name: ${{!startsWith(github.ref, 'refs/tags/') && 'nightly' || null}}
+          # TODO add instructions about using cosign to verify binary artifact
           append_body: true
           body: |
             <hr />
 
-            ## Check binary attestation at [here](${{ steps.attest.outputs.attestation-url }})
+            ### Check binary attestation at [here](${{ steps.attest.outputs.attestation-url }})