Policy Engines (OPA, Cerbos, Cedar)

Overview

Policy engines externalize authorization logic from application code, enabling centralized governance and consistent enforcement.

Engine Roles

• OPA: general policy evaluation with Rego
• Cerbos: authorization-focused policy service
• Cedar: policy language used in AWS authorization contexts

flowchart LR
    A[Application Request] --> B[Policy Decision Point]
    B --> C[OPA or Cerbos or Cedar]
    C --> D[Allow or Deny]

Practical Example

{
  "principal": "user:123",
  "resource": "invoice:789",
  "action": "read"
}

Policy engine returns a decision with optional reasons.

Production Example

Large platforms use policy engines to enforce consistent access decisions across APIs, admin portals, and background workers.

Common Pitfalls

• Policy and application data models diverging
• No decision logs for audits
• Excessive network latency in authorization path

Key Takeaways

• Policy engines improve consistency and maintainability of authorization.
• Centralized decisions support stronger governance.
• Performance and observability are key implementation concerns.