feat(release): sign and attest published docker images (#480)

Every published Sencho Docker image is now signed with Sigstore cosign
using GitHub Actions keyless OIDC, and ships with an embedded SBOM plus
SLSA provenance attestation attached as OCI referrers on the image.
Users can verify the signature and inspect the attestations themselves
before pulling an image into production.

  cosign verify saelix/sencho:<tag> \
    --certificate-identity-regexp "https://github.com/AnsoCode/Sencho/.*" \
    --certificate-oidc-issuer https://token.actions.githubusercontent.com

The release pipeline now also publishes a new moving minor tag
(saelix/sencho:X.Y, e.g. 0.42) alongside the existing latest and
immutable X.Y.Z tags, so operators who want the latest patch on a given
minor line can pin without chasing every release. Since every 0.x minor
is potentially breaking, the {{major}}-only tag is deferred until 1.0.

cosign is installed via the sigstore/cosign-installer action pinned to
a full commit SHA. The signing step batches every tag produced by
metadata-action into a single cosign invocation pinned to the built
digest, so all tags resolve to the same manifest and we save N-1
Rekor/Fulcio round trips. The job declares id-token: write so the
ambient OIDC token can be minted.

A new docs page (docs/reference/verifying-images.mdx) walks users
through installing cosign, verifying an image, and inspecting the SBOM
and provenance with docker buildx imagetools. A note calls out that
signatures start shipping with v0.43.0, so older images failing
verification is expected behavior and not tampering.

.github/workflows/docker-publish.yml

@@ -17,6 +17,8 @@ jobs:
     timeout-minutes: 30
     permissions:
       contents: read
+      # Required for cosign keyless signing via GitHub OIDC.
+      id-token: write
     steps:
       - name: Check out the repo
         uses: actions/checkout@v6
@@ -35,16 +37,27 @@ jobs:
           username: ${{ secrets.DOCKERHUB_USERNAME }}
           password: ${{ secrets.DOCKERHUB_TOKEN }}
 
+      - name: Install cosign
+        uses: sigstore/cosign-installer@cad07c2e89fa2edd6e2d7bab4c1aa38e53f76003 # v4.1.1
+
       - name: Extract metadata (tags, labels) for Docker
         id: meta
         uses: docker/metadata-action@v6
         with:
           images: saelix/sencho
+          # On a v-tag push we publish:
+          #   latest           always points at the newest release
+          #   X.Y.Z            the immutable semver tag
+          #   X.Y              moving minor tag for users who want latest patch
+          # The pre-1.0 constraint hides the {{major}}-only tag until we ship 1.0,
+          # since on 0.x every minor is potentially breaking.
           tags: |
             type=raw,value=latest,enable=${{ startsWith(github.ref, 'refs/tags/v') }}
             type=semver,pattern={{version}},enable=${{ startsWith(github.ref, 'refs/tags/v') }}
+            type=semver,pattern={{major}}.{{minor}},enable=${{ startsWith(github.ref, 'refs/tags/v') }}
 
       - name: Build and push Docker image
+        id: build
         uses: docker/build-push-action@v7
         with:
           context: .
@@ -54,3 +67,32 @@ jobs:
           labels: ${{ steps.meta.outputs.labels }}
           cache-from: type=registry,ref=saelix/sencho:buildcache
           cache-to: type=registry,ref=saelix/sencho:buildcache,mode=max
+          # SBOM + provenance attestations are embedded as OCI referrers on the
+          # published image. Inspect with: docker buildx imagetools inspect <img>
+          sbom: true
+          provenance: mode=max
+
+      - name: Sign published image with cosign (keyless)
+        # Signs every tag produced by metadata-action using the ambient GitHub
+        # OIDC token. No private keys, no secrets. Users verify with:
+        #   cosign verify saelix/sencho:<tag> \
+        #     --certificate-identity-regexp "https://github.com/AnsoCode/Sencho/.*" \
+        #     --certificate-oidc-issuer https://token.actions.githubusercontent.com
+        env:
+          TAGS: ${{ steps.meta.outputs.tags }}
+          DIGEST: ${{ steps.build.outputs.digest }}
+        run: |
+          # Build a single cosign invocation with every tag pinned to the digest.
+          # All tags resolve to the same manifest, so one call signs them all and
+          # saves N-1 Rekor/Fulcio round trips. On workflow_dispatch $TAGS is empty
+          # and the refs array stays empty, so we no-op cleanly.
+          refs=()
+          while IFS= read -r tag; do
+            [ -n "$tag" ] || continue
+            refs+=("${tag}@${DIGEST}")
+          done <<< "$TAGS"
+          if [ ${#refs[@]} -gt 0 ]; then
+            cosign sign --yes "${refs[@]}"
+          else
+            echo "No tags to sign (likely a workflow_dispatch run on a non-tag ref)."
+          fi

CHANGELOG.md

@@ -48,6 +48,14 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   Large payloads like `/api/templates` shrink roughly 5x on the wire, with
   Server-Sent Event streams explicitly excluded so real-time log tails and system
   metrics are not buffered.
+* **release:** sign every published Docker image with Sigstore cosign keyless
+  signing, and embed an SBOM plus SLSA provenance attestation as OCI referrers on
+  the image. Users can now independently verify that a pulled image came from the
+  official GitHub Actions build pipeline (see the new "Verifying Docker Images"
+  reference page in the docs). The release pipeline also publishes a new moving
+  minor tag `saelix/sencho:X.Y` alongside the existing `latest` and immutable
+  `X.Y.Z` tags, so operators who want the latest patch on a given minor line can
+  pin without chasing every release.
 
 ### Fixed
 

docs/docs.json

@@ -125,6 +125,7 @@
             "pages": [
               "features/node-compatibility",
               "reference/settings",
+              "reference/verifying-images",
               "reference/contact",
               "reference/security-advisories"
             ]

docs/reference/verifying-images.mdx

@@ -0,0 +1,81 @@
+---
+title: Verifying Docker Images
+description: Verify that the Sencho image you pulled was built and signed by the official GitHub Actions pipeline.
+---
+
+Every published Sencho Docker image is signed by the official GitHub Actions pipeline using [Sigstore cosign](https://docs.sigstore.dev/) keyless signing. The signature is backed by a short-lived certificate issued by Sigstore's public Fulcio certificate authority, tied to the GitHub Actions workflow run that produced the image. You can verify this signature yourself before pulling the image into production.
+
+Every image also ships with an embedded SBOM (Software Bill of Materials) and [SLSA](https://slsa.dev) (Supply-chain Levels for Software Artifacts) provenance attestation, so you can inspect exactly what went into the image and which workflow run built it.
+
+<Note>
+  Image signing is available starting with Sencho **v0.43.0**. Earlier releases do not ship a cosign signature; running `cosign verify` against them will fail, which is expected and does not indicate tampering. If you are on an older version, the first step is to upgrade.
+</Note>
+
+## Why verify
+
+Verification guarantees:
+
+1. The image was built from the [AnsoCode/Sencho](https://github.com/AnsoCode/Sencho) repository on GitHub.
+2. The build ran inside a GitHub Actions workflow, not on someone's laptop.
+3. The image has not been tampered with between publish and pull.
+
+<Note>
+  Verification is optional. If you skip it, Sencho still works exactly the same; you are just trusting Docker Hub to deliver the right bytes. Verification adds a second independent check.
+</Note>
+
+## Install cosign
+
+[cosign](https://docs.sigstore.dev/system_config/installation/) is a single static binary. Install it once on any machine you use to pull Sencho.
+
+<CodeGroup>
+
+```bash macOS (Homebrew)
+brew install cosign
+```
+
+```bash Linux (binary)
+curl -Lo cosign https://github.com/sigstore/cosign/releases/latest/download/cosign-linux-amd64
+chmod +x cosign
+sudo mv cosign /usr/local/bin/
+```
+
+```bash Windows (Scoop)
+scoop install cosign
+```
+
+</CodeGroup>
+
+## Verify a released image
+
+Replace `<tag>` with the version you intend to pull, for example `0.42.7`, `0.42`, or `latest`.
+
+```bash
+cosign verify saelix/sencho:<tag> \
+  --certificate-identity-regexp "https://github.com/AnsoCode/Sencho/.*" \
+  --certificate-oidc-issuer https://token.actions.githubusercontent.com
+```
+
+A successful verification prints the signature, the Rekor transparency log entry, and the certificate that signed it. If the image is not signed by the official Sencho pipeline, the command exits with a non-zero status and you should not run that image.
+
+## Inspect the SBOM and provenance
+
+Both the SBOM and SLSA provenance are attached to the published image as [OCI referrers](https://docs.docker.com/build/attestations/attestation-storage/). You can inspect them with `docker buildx imagetools`:
+
+```bash
+docker buildx imagetools inspect saelix/sencho:<tag> --format "{{json .SBOM}}"
+docker buildx imagetools inspect saelix/sencho:<tag> --format "{{json .Provenance}}"
+```
+
+The SBOM lists every package baked into the image with versions and licenses. The provenance records the exact GitHub Actions workflow run, commit SHA, and builder that produced it.
+
+## Available tags
+
+Each release publishes two moving tags plus one immutable tag, so you can choose how aggressively you want to track updates:
+
+| Tag | Example | Updates on |
+|---|---|---|
+| `latest` | `saelix/sencho:latest` | Every release |
+| `X.Y` | `saelix/sencho:0.42` | Every patch release in the `0.42.x` line |
+| `X.Y.Z` | `saelix/sencho:0.42.7` | Never (immutable) |
+
+For production, pin to `X.Y.Z` or `X.Y` and verify the signature on every pull. For staging or development, `latest` is fine.