add vulnerability scanning github action (#11096)

Adds a GitHub action that will run `snyk` and `trivy` scans against PRs
and comment on the PR if a high or critical vulnerability is found

.github/workflows/vulnerability-scan.yml

@@ -0,0 +1,90 @@
+name: PR Vulnerability Scan
+on: pull_request
+
+permissions:
+  pull-requests: write
+  contents: write
+
+jobs:
+  snyk:
+    name: Snyk Scan
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@master
+      - name: Run Snyk to check for vulnerabilities
+        uses: snyk/actions/golang@master
+        continue-on-error: true # To make sure that PR comment is made
+        env:
+          SNYK_TOKEN: ${{ secrets.SNYK_TOKEN }}
+        with:
+          command: test
+          args: --severity-threshold=high --json-file-output=snyk.json
+
+      - name: Prepare Snyk message
+        run: |
+          echo "Snyk scan found the following vulnerabilities:" > snyk.txt
+
+      - name: Format Snyk Message
+        uses: sergeysova/jq-action@v2
+        continue-on-error: true
+        with:
+          cmd: jq -r  '.vulnerabilities[] | "* **\(.severity)** - [\(.identifiers.CVE[0])] \(.title) in `\(.moduleName)` v\(.version). Fixed in \(.fixedIn)"' snyk.json >> snyk.txt
+
+      - name: Determine whether to comment
+        continue-on-error: true
+        id: should-comment
+        run: |
+          if [[ $(wc -l < snyk.txt) -gt 1 ]]; then exit 0; fi
+          exit 1
+
+      - name: Comment on PR with Snyk scan results
+        uses: mshick/add-pr-comment@v2
+        if: ${{ steps.should-comment.outcome == 'success' }}
+        with:
+          message-id: snyk-${{ github.event.number }}
+          message-path: snyk.txt
+  trivy:
+    name: Trivy Scan
+    runs-on: ubuntu-20.04
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v3
+
+      - name: Build Loki Image
+        run: |
+          IMAGE_TAG="$(./tools/image-tag)"
+          make loki-image
+          echo "IMAGE_TAG=${IMAGE_TAG}" >> $GITHUB_ENV
+
+      - name: Run Trivy vulnerability scanner
+        uses: aquasecurity/trivy-action@master
+        with:
+          image-ref: "docker.io/grafana/loki:${{ env.IMAGE_TAG }}"
+          format: "json"
+          output: "trivy.json"
+          severity: "CRITICAL,HIGH"
+
+      - name: Prepare Trivy Message
+        run: |
+          echo "Trivy scan found the following vulnerabilities:" > trivy.txt
+
+      - name: Format Trivy Message
+        uses: sergeysova/jq-action@v2
+        continue-on-error: true
+        with:
+          cmd: jq -r '.Results[] | select(.Vulnerabilities != null) | .Vulnerabilities[] | "* **\(.Severity)** [\(.Title)](\(.PrimaryURL)) in `\(.PkgName)` v\(.InstalledVersion). Fixed in v\(.FixedVersion)"' trivy.json >> trivy.txt
+
+      - name: Determine whether to comment
+        continue-on-error: true
+        id: should-comment
+        run: |
+          if [[ $(wc -l < trivy.txt) -gt 1 ]]; then exit 0; fi
+          exit 1
+
+      - name: Comment on PR with Trivy scan results
+        uses: mshick/add-pr-comment@v2
+        if: ${{ steps.should-comment.outcome == 'success' }}
+        with:
+          message-id: trivy-${{ github.event.number }}
+          message-path: trivy.txt