ci: print this repo's OIDC claim format

.github/workflows/oidc-claims.yaml

@@ -0,0 +1,31 @@
+name: oidc-claims
+
+on:
+  pull_request:
+    branches: [main]
+
+permissions:
+  contents: read
+  id-token: write
+
+jobs:
+  claims:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Print selected OIDC claims
+        run: |
+          set -euo pipefail
+          RESP="$(curl -fsS -H "Authorization: bearer ${ACTIONS_ID_TOKEN_REQUEST_TOKEN}" \
+            "${ACTIONS_ID_TOKEN_REQUEST_URL}&audience=sts.amazonaws.com")"
+          TOKEN="$(printf '%s' "${RESP}" | jq -r .value)"
+          echo "::add-mask::${TOKEN}"
+          PAYLOAD="$(printf '%s' "${TOKEN}" | cut -d. -f2)"
+          unset TOKEN RESP
+          python3 -c '
+          import base64, json, sys
+          raw = sys.argv[1]
+          raw += "=" * (-len(raw) % 4)
+          data = json.loads(base64.urlsafe_b64decode(raw))
+          keep = ["sub", "job_workflow_ref", "workflow_ref", "repository", "repository_id", "repository_owner_id"]
+          print(json.dumps({k: data.get(k) for k in keep}, indent=2))
+          ' "${PAYLOAD}"