Least Privilege & Zero Trust Architecture: Principles, microsegmentation, and identity verification.

Beyond Castle-and-Moat Security

Traditional "castle-and-moat" security assumed that once traffic passed through the corporate VPN or edge firewall, internal network traffic was inherently trustworthy. Modern Zero Trust operates on one non-negotiable rule: "Never trust, always verify."

Legacy Castle-and-Moat (Vulnerable):
[ Attackers Breach VPN ] ===> Full access to internal DBs, Redis, and APIs!

Zero Trust Architecture:
[ Client / Service ]
        |
        v 1. Verify Identity (mTLS X.509 + SPIFFE)
[ Service A ] -------------------------+
                                       | 2. Enforce Least Privilege RBAC
                                       v
                                 [ Service B ]
                                       | 3. Encrypt & Log Transaction
                                       v
                                 [ PostgreSQL ]

Core Zero Trust Tenets

1. Explicit Identity Verification: Every service-to-service call verifies mutual TLS (mTLS) with cryptographically validated X.509 certificates and SPIFFE IDs (e.g. spiffe://cluster.local/ns/prod/sa/order-service).
2. Least Privilege Access: Grant only the bare minimum permissions needed to complete a task. An API worker should only have SELECT, INSERT on its specific table—never DROP, ALTER, or cluster-admin rights.
3. Assume Breach: Design assuming an attacker is already inside the internal network. Segment networks using Kubernetes NetworkPolicies so that an RCE in the frontend pod cannot establish a TCP connection to the internal payment ledger.