Approach overview
I would design a layered API Gateway platform (edge + control plane) that separates public traffic from partner/internal traffic while enforcing centralized security, observability, and policy management.
Authentication & Authorization
- Public APIs: OAuth2 with Authorization Code / PKCE for apps; issue short-lived JWT access tokens validated at gateway (local JWT verification) and optionally introspection for revocation.
- Partner APIs: mTLS + OAuth2 client_credentials or issued API keys with rotation; for high-trust partners require mutual TLS and scoped JWTs.
- Fine-grained authz via claims -> RBAC/ABAC policies evaluated in gateway or downstream IAM.
Rate limiting & SLA/monetization
- Token-bucket rate limits enforced at gateway using distributed store (Redis/Envoy rate-limit service) with per-customer, per-plan, and per-endpoint keys.
- Support tiers: free (low RPS, burst), standard, premium (higher RPS, SLA: 99.95%). Map tiers in subscription catalog; billing events emitted to monetization system.
- Circuit-breakers and quota enforcement with graceful 429/503 semantics and webhook/alerts for overage.
Request validation & TLS
- Validate schema (JSON Schema), size limits, required headers, and reject early. Use WAF rules for OWASP protections.
- TLS termination at edge/load balancer; re-encrypt to services (TLS origination). For partners requiring mTLS, terminate client cert at gateway and forward identity.
Observability
- Structured logging, distributed tracing (W3C Trace-Context), metrics (Prometheus), and alerting. Capture per-tenant metrics, latency percentiles, error budgets.
- Central dashboard for API product owners, automated SLA reporting, and audit logs for security/compliance.
Operational / trade-offs
- Use managed API Gateway (e.g., APIM/Envoy Kuma/AWS API GW + custom proxies) to reduce ops burden; augment with custom control plane for monetization and policy lifecycle.
- Balance local JWT checks (low latency) vs introspection (revocation flexibility).
- Start with conservative rate limits and evolve via telemetry.
This design provides secure, scalable enforcement, clear separation for partners, and built-in hooks for monetization and SLA differentiation.
