fix: validate universe domain input to prevent SSRF credential leak

[adilburaksen]

Summary

The universe input is interpolated directly into the Cloud Functions API endpoint:

cloudfunctions: 'https://cloudfunctions.{universe}/v2',

Setting universe: attacker.com routes all API calls — including Bearer GCP access tokens — to cloudfunctions.attacker.com.

Fix

Validates universe against known-safe patterns before use:

if (!/^([a-z0-9-]+\.)*googleapis\.com$/.test(universe)) {
  throw new Error(`Invalid universe domain "${universe}": ...`);
}

Allows googleapis.com (default) and Trusted Partner Cloud subdomains like us-central1.rep.googleapis.com. Blocks arbitrary hostnames.

Related

Companion PR for upload-cloud-storage: google-github-actions/upload-cloud-storage#404
Same class, same root cause in expandUniverseEndpoints.