Is Your Auth Implementation Predictable, Testable, and Isolated?

Type: Structure, 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.

---

🔗 Related Perspectives

• Is Your API Permission Design Explicit and Secure?
• Is Authorization Modeled as Domain Behavior—or Just Filtered in the UI?
• Are Security Risks Considered?
• Does Your System Prevent Privilege Escalation?