Cloud Sql Postgres Shared Ca Tls Verification

What Complete Server Identity Verification Is

Server identity verification with TLS ensures that the client not only validates that the database server's certificate was signed by a trusted Certificate Authority (CA), but also validates that the certificate's Subject Alternative Name (SAN) matches the exact hostname to which the client is connecting.

How It Meets the Requirements

• Shared CA Identity Assurance: When a Cloud SQL instance uses a shared CA, multiple database instances share the same root/intermediate CA. Validating only the CA chain is insufficient because any instance signed by that shared CA would be trusted. Enforcing hostname verification against the instance-specific SAN guarantees the identity of the specific target instance.
• Private Service Connect (PSC) Resolution: Cloud SQL instances with a shared CA contain the instance DNS name (e.g., INSTANCE_UID.PROJECT_DNS_LABEL.REGION_NAME.sql.goog.) in the server certificate's SAN field. Registering this name in a VPC private Cloud DNS zone ensures that private clients correctly resolve the DNS name to the PSC endpoint IP.
• Client Verification Mode: Setting sslmode=verify-full in PostgreSQL client drivers enforces both trusted CA validation and strict SAN hostname matching.

Key Advantages

• MitM and Spoofing Prevention: Prevents malicious or misconfigured instances sharing the same root CA from intercepting traffic.
• Private Route Integration: Operates seamlessly inside private VPC networks via Cloud DNS and Private Service Connect.
• Zero-Trust Compliance: Meets strict regulatory standards for data-in-transit authenticity and non-repudiation.

Why This Is Optimal

This solution properly aligns DNS resolution, certificate SAN metadata, and client TLS enforcement (sslmode=verify-full), providing end-to-end cryptographic trust.