feat: make Helm releases independently verifiable

Helm ships binaries via Azure with no cosign, SBOM, or provenance,
and the upstream release.yml is gated to helm/helm so it can't be
exercised on a fork. This adds a self-contained release-signed
workflow plus the .goreleaser.yaml archive/sbom/checksum/signs
config it needs, modeled on goreleaser/example-secure, to demo the
full pipeline end-to-end before proposing it upstream.

Signed-off-by: Benoit Tigeot <benoit.tigeot@lifen.fr>

.github/workflows/release-signed.yml

@@ -0,0 +1,53 @@
+#
+# PoC: signed release with SBOMs and build provenance.
+# Modeled on https://github.com/goreleaser/example-secure
+#
+name: release-signed
+
+on:
+  push:
+    tags:
+      - "v*"
+
+permissions:
+  contents: write # needed to write releases
+  id-token: write # needed for keyless signing
+  attestations: write # needed for provenance
+
+jobs:
+  release:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout source code
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # pin@v7.0.1
+        with:
+          fetch-depth: 0
+          persist-credentials: false
+
+      - name: Add variables to environment file
+        run: cat ".github/env" >> "$GITHUB_ENV"
+
+      - name: Setup Go
+        uses: actions/setup-go@b7ad1dad31e06c5925ef5d2fc7ad053ef454303e # pin@7.0.0
+        with:
+          go-version: '${{ env.GOLANG_VERSION }}'
+          check-latest: true
+
+      - name: Install Cosign
+        uses: sigstore/cosign-installer@cad07c2e89fa2edd6e2d7bab4c1aa38e53f76003 # v4.1.1
+
+      - name: Install Syft
+        uses: anchore/sbom-action/download-syft@e22c389904149dbc22b58101806040fa8d37a610 # v0.24.0
+
+      - name: Run GoReleaser
+        uses: goreleaser/goreleaser-action@e24998b8b67b290c2fa8b7c14fcfa7de2c5c9b8c # v7.1.0
+        with:
+          version: "~> v2"
+          args: release --clean
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Attest build provenance
+        uses: actions/attest-build-provenance@a2bbfa25375fe432b6a289bc6b6cd05ecd0c4c32 # v4.1.0
+        with:
+          subject-checksums: ./_dist/checksums.txt

.goreleaser.yaml

@@ -55,14 +55,57 @@ builds:
       - goos: windows
         goarch: loong64
     main: ./cmd/helm
-    no_unique_dist_dir: true
-    binary: "{{ .Os }}-{{ .Arch }}/helm"
+    binary: helm
+    mod_timestamp: "{{ .CommitTimestamp }}"
     ldflags:
-      - "{{ .Env.LDFLAGS }}"
+      - -w -s
+      - -extldflags "-static"
+      - -X helm.sh/helm/v4/internal/version.version={{ .Tag }}
+      - -X helm.sh/helm/v4/internal/version.metadata=
+      - -X helm.sh/helm/v4/internal/version.gitCommit={{ .FullCommit }}
+      - -X helm.sh/helm/v4/internal/version.gitTreeState=clean
     flags:
       - -trimpath
     dir: .
 
+source:
+  enabled: true
+  name_template: "{{ .ProjectName }}.src"
+
+archives:
+  - formats:
+      - tar.gz
+    format_overrides:
+      - goos: windows
+        formats:
+          - zip
+    name_template: "helm-{{ .Tag }}-{{ .Os }}-{{ .Arch }}"
+    wrap_in_directory: true
+    files:
+      - LICENSE
+      - README.md
+    builds_info:
+      mtime: "{{ .CommitTimestamp }}"
+
+sboms:
+  - artifacts: archive
+  - id: source
+    artifacts: source
+
+checksum:
+  name_template: "checksums.txt"
+
+signs:
+  - cmd: cosign
+    signature: "${artifact}.sigstore.json"
+    args:
+      - sign-blob
+      - "--bundle=${signature}"
+      - "${artifact}"
+      - "--yes"
+    artifacts: checksum
+    output: true
+
 snapshot:
   version_template: "{{ if index .Env \"GORELEASER_CURRENT_TAG\" }}{{ .Env.GORELEASER_CURRENT_TAG }}{{ else }}{{ incpatch .Version }}-next{{ end }}"
 

Makefile

@@ -172,7 +172,7 @@ $(GOIMPORTS):
 .PHONY: build-cross
 build-cross: LDFLAGS += -extldflags "-static"
 build-cross: $(GORELEASER)
-	LDFLAGS='$(LDFLAGS)' $(GORELEASER) build --snapshot --clean
+	$(GORELEASER) build --snapshot --clean
 
 .PHONY: dist
 dist: