chore: add consolidated SBOM generation workflow

.github/workflows/sbom.yml

@@ -0,0 +1,96 @@
+name: Generate SBOM
+
+# Generates and attaches an SPDX SBOM to the GitHub release for the pushed
+# version tag.  Runs only on vX.Y.Z tag pushes; the SBOM asset is uploaded
+# (or replaced) via the GitHub Releases API.  Idempotent: if the asset
+# already exists it is deleted and re-uploaded with fresh scan output.
+
+on:
+  push:
+    tags:
+      - "v*"
+
+permissions: {}
+
+concurrency:
+  group: sbom-${{ github.ref }}
+  cancel-in-progress: false
+
+jobs:
+  generate-sbom:
+    name: Generate and Attach SBOM
+    runs-on: ubuntu-latest
+    timeout-minutes: 30
+    permissions:
+      contents: write # upload SBOM asset to the GitHub release
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262 # v4.4.0
+        with:
+          persist-credentials: false
+
+      - name: Install Syft (pinned version with checksum verification)
+        env:
+          SYFT_VERSION: "1.41.0"
+        run: |
+          curl -sSfL -o syft.tar.gz \
+            "https://github.com/anchore/syft/releases/download/v${SYFT_VERSION}/syft_${SYFT_VERSION}_linux_amd64.tar.gz"
+          curl -sSfL -o syft_checksums.txt \
+            "https://github.com/anchore/syft/releases/download/v${SYFT_VERSION}/syft_${SYFT_VERSION}_checksums.txt"
+          # Verify the downloaded archive against the published checksum for this exact asset.
+          EXPECTED=$(awk '$2 == "syft_'${SYFT_VERSION}'_linux_amd64.tar.gz" {print $1}' syft_checksums.txt)
+          echo "${EXPECTED}  syft.tar.gz" | sha256sum -c -
+          tar -xzf syft.tar.gz syft
+          sudo mv syft /usr/local/bin/syft
+          rm -f syft.tar.gz syft_checksums.txt
+
+      - name: Generate SBOM (SPDX format)
+        run: |
+          syft . -o spdx-json=sbom.spdx.json
+
+      - name: Find release ID for the pushed tag
+        id: release
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          TAG_NAME="${GITHUB_REF#refs/tags/}"
+          RELEASE_ID=$(curl -s -H "Authorization: token ${GITHUB_TOKEN}" \
+            "https://api.github.com/repos/${GITHUB_REPOSITORY}/releases/tags/${TAG_NAME}" \
+            | jq -r '.id')
+
+          if [ -z "${RELEASE_ID}" ] || [ "${RELEASE_ID}" = "null" ]; then
+            echo "release_id=" >> "${GITHUB_OUTPUT}"
+          else
+            echo "release_id=${RELEASE_ID}" >> "${GITHUB_OUTPUT}"
+          fi
+
+      - name: Check for existing SBOM asset and upload
+        if: steps.release.outputs.release_id != '' && steps.release.outputs.release_id != 'null'
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          RELEASE_ID: ${{ steps.release.outputs.release_id }}
+        run: |
+          # Check if an SBOM asset with this name already exists in the release
+          ASSET_ID=$(curl -s -H "Authorization: token ${GITHUB_TOKEN}" \
+            "https://api.github.com/repos/${GITHUB_REPOSITORY}/releases/${RELEASE_ID}/assets" \
+            | jq -r ".[] | select(.name == \"sbom.spdx.json\") | .id")
+
+          if [ -n "${ASSET_ID}" ] && [ "${ASSET_ID}" != "null" ]; then
+            # Delete existing SBOM asset so we can re-upload the fresh scan
+            curl -s -X DELETE -H "Authorization: token ${GITHUB_TOKEN}" \
+              "https://api.github.com/repos/${GITHUB_REPOSITORY}/releases/assets/${ASSET_ID}" > /dev/null
+            echo "Deleted existing sbom.spdx.json asset"
+          fi
+
+          # Upload the SBOM as a release asset
+          curl -s -X POST -H "Authorization: token ${GITHUB_TOKEN}" \
+            -H "Content-Type: application/spdx+json" \
+            --data-binary @sbom.spdx.json \
+            "https://uploads.github.com/repos/${GITHUB_REPOSITORY}/releases/${RELEASE_ID}/assets" > /dev/null
+          echo "Uploaded sbom.spdx.json to release ${RELEASE_ID}"
+
+      - name: Notify if no release found for tag
+        if: steps.release.outputs.release_id == '' || steps.release.outputs.release_id == 'null'
+        run: |
+          echo "::notice::No GitHub Release found for tag ${GITHUB_REF#refs/tags/}. The SBOM was generated at ./sbom.spdx.json but was not attached to a release. Ensure the tag was created by the release-please process or manually create a release draft."