Sign main branch Unified container builds with cosign (#325)

.github/workflows/build-unified.yml

@@ -34,6 +34,9 @@ jobs:
   build-docker:
     name: Build Docker image
     runs-on: ubuntu-22.04
+    permissions:
+      security-events: write
+      id-token: write
     steps:
       - name: Checkout Repository - workflow_call
         if: ${{ inputs.is_workflow_call == true }}
@@ -145,9 +148,10 @@ jobs:
           repository: bitwarden/server
           token: ${{ steps.retrieve-secret-pat.outputs.github-pat-bitwarden-devops-bot-repo-scope }}
           ref: ${{ steps.server-branch-name.outputs.server_branch }}
-          path: 'server'
+          path: "server"
 
       - name: Build and push Docker image
+        id: build-docker
         uses: docker/build-push-action@48aba3b46d1b1fec4febb7c5d0c644b249a11355 # v6.10.0
         with:
           context: .
@@ -161,6 +165,36 @@ jobs:
           secrets: |
             "GH_PAT=${{ steps.retrieve-secret-pat.outputs.github-pat-bitwarden-devops-bot-repo-scope }}"
 
+      - name: Install Cosign
+        if: inputs.is_workflow_call == true && github.ref == 'refs/heads/main'
+        uses: sigstore/cosign-installer@dc72c7d5c4d10cd6bcb8cf6e3fd625a9e5e537da # v3.7.0
+
+      - name: Sign image with Cosign
+        if: inputs.is_workflow_call == true && github.ref == 'refs/heads/main'
+        env:
+          DIGEST: ${{ steps.build-docker.outputs.digest }}
+          TAGS: ${{ steps.tag-list.outputs.tags }}
+        run: |
+          IFS="," read -a tags <<< "${TAGS}"
+          images=""
+          for tag in "${tags[@]}"; do
+            images+="${tag}@${DIGEST} "
+          done
+          cosign sign --yes ${images}
+
+      - name: Scan Docker image
+        id: container-scan
+        uses: anchore/scan-action@5ed195cc06065322983cae4bb31e2a751feb86fd # v5.2.0
+        with:
+          image: ${{ steps.tag-list.outputs.primary_tag }}
+          fail-build: false
+          output-format: sarif
+
+      - name: Upload Grype results to GitHub
+        uses: github/codeql-action/upload-sarif@662472033e021d55d94146f66f6058822b0b39fd # v3.27.0
+        with:
+          sarif_file: ${{ steps.container-scan.outputs.sarif }}
+
       - name: Log out of Docker and disable Docker Notary
         if: ${{ env.is_publish_branch == 'true' }}
         run: |