add cosign

Author: g-bgg

.github/workflows/docker.yaml

@@ -28,6 +28,9 @@ jobs:
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v2
 
+      - name: Install cosign
+        uses: sigstore/cosign-installer@v3
+
       - name: Log in to GHCR
         uses: docker/login-action@v3
         with:
@@ -54,3 +57,8 @@ jobs:
             controlplane/netassertv2-l4-client:latest
             ${{ env.GH_REGISTRY }}/controlplaneio/${{ env.IMAGE_NAME }}:${{ github.ref_name }}
             ${{ env.GH_REGISTRY }}/controlplaneio/${{ env.IMAGE_NAME }}:latest
+      
+      - name: Sign artifact
+        run: cosign sign --yes $DIGEST_URL
+        env:
+          DIGEST_URL: ${{ steps.buildpush.outputs.digest }}