Introduction: Why Zero Trust Matters for APIsAPIs are the digital nervous system of modern software. They connect microservices, mobile apps, and external partners. But every connection is a potential attack surface. **Zero Trust Architecture (ZTA)** is no longer optional for high-value or high-risk APIs—it’s a practical necessity.## Understanding Zero Trust PrinciplesZero Trust isn't a product. It's a security philosophy with some battle-tested rules.### Never Trust, Always VerifyEvery request—whether inside your network or from the public internet—must be authenticated and authorized.### Assume BreachOperate as if an attacker is already in your system. This drives risk-aware design: segment data and services, validate every call.## Where REST APIs Fit in Zero Trust### Public APIsPublic endpoints (e.g., payment, weather, exchange rates) face constant probing. Zero Trust adds layered controls to slow down and detect malicious behavior.### Internal MicroservicesIntra-service traffic also needs Zero Trust. No “safe zone” should exist inside your architecture.## Core Zero Trust Techniques for REST APIs### Strong AuthenticationImplement protocols like **OAuth 2.0** with short-lived **JWTs**. Issue tokens with scoped permissions, not blanket admin rights.### Fine-Grained AuthorizationEnforce authorization at the resource and action level. Use attribute-based access control (ABAC) for contextual checks.### Mutual TLS (mTLS)Require clients and servers to authenticate each other via TLS certificates. This secures service-to-service calls.### Continuous VerificationDon’t assume that once a token is issued, the user or service remains safe. Revalidate sessions periodically.## Common Pitfalls When Combining REST APIs and Zero Trust- **Over-permissive scopes**: Tokens should never carry more privilege than necessary.
