feat: Add GitHub Attestation, prepare for signed releases

.github/workflows/build-containers.yml

@@ -93,6 +93,8 @@ jobs:
       contents: read
       packages: write
       id-token: write # required for keyless cosign signing via OIDC
+      attestations: write
+      artifact-metadata: write
     strategy:
       fail-fast: false
       matrix:
@@ -186,6 +188,13 @@ jobs:
           path: digest-*.json
           retention-days: 1
 
+      - name: Attest image build provenance
+        if: needs.pr-author-permission.outputs.is_collaborator == 'true'
+        uses: actions/attest@508db95dd578ae2727ebd6217d5ba78e4fbda05d # v4.2.1
+        with:
+          subject-name: ${{ env.REGISTRY }}/${{ steps.image.outputs.name }}
+          subject-digest: ${{ steps.build_and_push.outputs.digest }}
+          push-to-registry: true
 
   post-build:
     name: Post-Build Digest Collector

.github/workflows/prod.yml

@@ -48,14 +48,28 @@ jobs:
     name: Release
     needs: publish
     runs-on: ubuntu-latest
+    permissions:
+      contents: write
+      id-token: write
 
     steps:
       - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0
 
       - uses: actions/download-artifact@3e5f45b2cfb9172054b4087a40e8e0b5a5461e7c
         with:
-          name: '*-signed'
+          pattern: '*-signed'
           path: packages
+          merge-multiple: true
+
+      - name: Install cosign
+        uses: sigstore/cosign-installer@6f9f17788090df1f26f669e9d70d6ae9567deba6 # v4.1.2
+
+      - name: Sign release packages
+        working-directory: packages
+        run: |
+          for package in *.deb; do
+            cosign sign-blob --yes --bundle "${package}.sigstore.json" "${package}"
+          done
 
       - name: Create release
         working-directory: packages
@@ -68,4 +82,5 @@ jobs:
             --target ${{ github.sha }} \
             --generate-notes \
             --latest \
-            *.deb
+            *.deb \
+            *.sigstore.json