ci(actions): add GHCR mirroring and cosign signing for Docker images

- mirror images from Docker Hub to GHCR using skopeo (preserves multi-arch manifests)
- login to GHCR via docker/login-action for signing/pushing
- install cosign and perform dual signing: keyless (OIDC) + key-based; verify signatures
- add required permissions for id-token/packages and reference necessary secrets

.github/workflows/cicd.yml

@@ -1,17 +1,37 @@
 name: CI/CD Pipeline
 
+# CI/CD workflow for building, publishing, mirroring, signing container images and building release binaries.
+# Actions are pinned to specific SHAs to reduce supply-chain risk. This workflow triggers on tag push events.
+
 permissions:
   contents: read
+  packages: write      # for GHCR push
+  id-token: write      # for Cosign Keyless (OIDC) Signing
+
+# Required secrets:
+# - DOCKER_HUB_USERNAME / DOCKER_HUB_ACCESS_TOKEN: push to Docker Hub
+# - GITHUB_TOKEN: used for GHCR login and OIDC keyless signing
+# - COSIGN_PRIVATE_KEY / COSIGN_PASSWORD / COSIGN_PUBLIC_KEY: for key-based signing
 
 on:
   push:
     tags:
       - "*"
 
+concurrency:
+  group: ${{ github.ref }}
+  cancel-in-progress: true
+
 jobs:
   release:
     name: Build and Release
     runs-on: amd64-runner
+    # Job-level timeout to avoid runaway or stuck runs
+    timeout-minutes: 120
+    env:
+      # Target images
+      DOCKERHUB_IMAGE: docker.io/${{ secrets.DOCKER_HUB_USERNAME }}/${{ github.event.repository.name }}
+      GHCR_IMAGE: ghcr.io/${{ github.repository_owner }}/${{ github.event.repository.name }}
 
     steps:
       - name: Checkout code
@@ -26,12 +46,14 @@ jobs:
       - name: Log in to Docker Hub
         uses: docker/login-action@5e57cd118135c172c3672efd75eb46360885c0ef # v3.6.0
         with:
+          registry: docker.io
           username: ${{ secrets.DOCKER_HUB_USERNAME }}
           password: ${{ secrets.DOCKER_HUB_ACCESS_TOKEN }}
 
       - name: Extract tag name
         id: get-tag
         run: echo "TAG=${GITHUB_REF#refs/tags/}" >> $GITHUB_ENV
+        shell: bash
 
       - name: Install Go
         uses: actions/setup-go@44694675825211faa026b3c33043df3e48a5fa00 # v6.0.0
@@ -47,15 +69,89 @@ jobs:
           else
             echo "main.go not found"
           fi
+        shell: bash
 
-            - name: Build and push Docker images
+      - name: Build and push Docker images (Docker Hub)
         run: |
           TAG=${{ env.TAG }}
           make docker-build-release tag=$TAG
+          echo "Built & pushed to: ${{ env.DOCKERHUB_IMAGE }}:${TAG}"
+        shell: bash
+
+      - name: Login in to GHCR
+        uses: docker/login-action@5e57cd118135c172c3672efd75eb46360885c0ef # v3.6.0
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Install skopeo + jq
+        # skopeo: copy/inspect images between registries
+        # jq: JSON parsing tool used to extract digest values
+        run: |
+          sudo apt-get update -y
+          sudo apt-get install -y skopeo jq
+          skopeo --version
+        shell: bash
+
+      - name: Copy tag from Docker Hub to GHCR
+        # Mirror the already-built image (all architectures) to GHCR so we can sign it
+        run: |
+          set -euo pipefail
+          TAG=${{ env.TAG }}
+          echo "Copying ${{ env.DOCKERHUB_IMAGE }}:${TAG} -> ${{ env.GHCR_IMAGE }}:${TAG}"
+          skopeo copy --all --retry-times 3 \
+            docker://$DOCKERHUB_IMAGE:$TAG \
+            docker://$GHCR_IMAGE:$TAG
+        shell: bash
+
+      - name: Install cosign
+        # cosign is used to sign and verify container images (key and keyless)
+        uses: sigstore/cosign-installer@faadad0cce49287aee09b3a48701e75088a2c6ad # v4.0.0
+
+      - name: Dual-sign and verify (GHCR & Docker Hub)
+        # Sign each image by digest using keyless (OIDC) and key-based signing,
+        # then verify both the public key signature and the keyless OIDC signature.
+        env:
+          TAG: ${{ env.TAG }}
+          COSIGN_PRIVATE_KEY: ${{ secrets.COSIGN_PRIVATE_KEY }}
+          COSIGN_PASSWORD: ${{ secrets.COSIGN_PASSWORD }}
+          COSIGN_PUBLIC_KEY: ${{ secrets.COSIGN_PUBLIC_KEY }}
+          COSIGN_YES: "true"
+        run: |
+          set -euo pipefail
+
+          issuer="https://token.actions.githubusercontent.com"
+          id_regex="^https://github.com/${{ github.repository }}/.+"  # accept this repo (all workflows/refs)
+
+          for IMAGE in "${GHCR_IMAGE}" "${DOCKERHUB_IMAGE}"; do
+            echo "Processing ${IMAGE}:${TAG}"
+
+            DIGEST="$(skopeo inspect --retry-times 3 docker://${IMAGE}:${TAG} | jq -r '.Digest')"
+            REF="${IMAGE}@${DIGEST}"
+            echo "Resolved digest: ${REF}"
+
+            echo "==> cosign sign (keyless) --recursive ${REF}"
+            cosign sign --recursive "${REF}"
+
+            echo "==> cosign sign (key) --recursive ${REF}"
+            cosign sign --key env://COSIGN_PRIVATE_KEY --recursive "${REF}"
+
+            echo "==> cosign verify (public key) ${REF}"
+            cosign verify --key env://COSIGN_PUBLIC_KEY "${REF}" -o text
+
+            echo "==> cosign verify (keyless policy) ${REF}"
+            cosign verify \
+              --certificate-oidc-issuer "${issuer}" \
+              --certificate-identity-regexp "${id_regex}" \
+              "${REF}" -o text
+          done
+        shell: bash
 
       - name: Build binaries
         run: |
           make go-build-release
+        shell: bash
 
       - name: Upload artifacts from /bin
         uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2