The question requires a secure channel without authentication. Option D uses an HTTP(S) load balancer with a Google-managed SSL certificate, which encrypts traffic via HTTPS, providing the necessary secure channel. Option C uses IAP, which requires authentication, contradicting the requirement. Option A incorrectly uses service account keys for encryption (they are for authentication) and lacks HTTPS. Option B changes the real-time setup to static exports, which doesn't meet the real-time requirement and may not ensure HTTPS. Thus, D is correct.