feat(ci): add SLSA L1 provenance attestation (OWASP A03)

.github/workflows/provenance.yml

@@ -0,0 +1,46 @@
+# =============================================================================
+# SLSA L1 — Provenance Attestation (OWASP A03: Supply Chain)
+# Generates signed provenance for build artifacts
+# =============================================================================
+
+name: SLSA Provenance Attestation
+
+on:
+  push:
+    branches: [main, develop]
+
+permissions:
+  contents: read
+  id-token: write   # Required for OIDC signing
+  attestations: write
+
+jobs:
+  provenance:
+    name: Generate Provenance Attestation
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Setup Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.11"
+
+      - name: Install build tools
+        run: python -m pip install --upgrade pip build
+
+      - name: Build package
+        run: python -m build
+
+      - name: Attest build provenance
+        uses: actions/attest-build-provenance@v2
+        with:
+          subject-path: dist/*
+
+      - name: Upload provenance artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: provenance
+          path: .attestation/
+          retention-days: 90

.github/workflows/verify-provenance.yml

@@ -0,0 +1,33 @@
+# =============================================================================
+# SLSA L1 — Verify Provenance Attestation (OWASP A03: Supply Chain)
+# Verifies that build artifacts have valid provenance
+# =============================================================================
+
+name: Verify Provenance
+
+on:
+  pull_request:
+    branches: [main, develop]
+
+permissions:
+  contents: read
+  attestations: read
+  id-token: write
+
+jobs:
+  verify:
+    name: Verify Source Provenance
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Verify attestation
+        run: |
+          # List attestations for this commit
+          BASE_SHA=$(git rev-parse origin/${{ github.base_ref }})
+          gh attestation verify "$BASE_SHA" \
+            --owner ${{ github.repository_owner }} \
+            --predicate-type https://slsa.dev/provenance/v1
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}