The correct approach involves securing the bucket and using least privilege. Enforcing public access prevention ensures the bucket cannot be made public, a Google best practice. Using a user-managed service account (instead of the default Compute Engine account) allows granular permissions. Granting the Storage Object Viewer role to this service account provides the necessary access without excessive privileges. Options A/B use the default service account (insecure), and C suggests signed URLs, which are unnecessary here as the app itself (not end-users) needs access.