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Is Your Auth Implementation Predictable, Testable, and Isolated?

Type: DeepDive
Category: Security
Audience: Engineers implementing login, session, token, or permissions in SaaS systems

🔍 What This Perspective Covers

Authentication (AuthN) and Authorization (AuthZ) are not features.
They are foundations—and when shaky, everything on top suffers.

⚠️ Auth Fragility Patterns

  • Auth logic split across middlewares, controllers, services
  • Manual JWT parsing or unclear claim propagation
  • Mixing login session state with API token flows
  • Test environments bypass auth logic, causing drift from prod
  • Inconsistent roles or scope propagation across services

✅ Better Auth Design Practices

  • Centralize auth verification into a testable, composable unit
  • Use middleware for identity extraction—but not decision logic
  • Define clear boundaries: AuthN (who?) vs AuthZ (can?)
  • Make roles, scopes, and tenants explicit in all internal requests
  • Test token expiration, claim tampering, and role confusion

🧠 Principle

You don’t need custom auth.
You need custom enforcement of clear intent.

❓ FAQ

  • Q: Should we roll our own auth?
    A: Rarely. Prefer platform-backed identity—but enforce your own permission boundaries.

  • Q: Can’t middleware do everything?
    A: Middleware should extract identity—not decide business intent.