Secure APIs: Authentication, Authorization and Rate Limiting

APIs are the backbone of modern software. To keep data safe and services reliable, you need a clear plan for authentication, authorization, and rate limiting. These three parts work together: authentication verifies who is calling, authorization decides what they can do, and rate limiting controls how fast they can go. Getting all three right reduces risk and improves user experience.

Authentication

There are several common options that fit different scenarios:

  • API keys: simple and fast for server-to-server calls, but they reveal only that the caller knows the key. They should be used with TLS and tied to an account or quota; rotate keys regularly.

  • OAuth 2.0 and access tokens: scalable for user and service accounts. Tokens expire and should be short-lived; use refresh tokens when needed. Prefer Authorization: Bearer tokens and store them securely.

  • JWTs: compact tokens that carry claims. Validate signature and issuer; avoid putting secrets in the token. Use short expiry and proper audience checks.

  • Mutual TLS: the client presents a certificate, offering strong identity for internal services.

Authorization

Authentication answers who you are; authorization answers what you can do. Define careful checks to follow least privilege:

  • Scopes and permissions: create fine-grained actions like read_orders or write_payments.

  • RBAC and ABAC: grant access by role or by attributes; apply these checks at the gateway or inside services.

  • Resource-level checks: verify both the token and the specific resource. Restrict access when possible and avoid wide open permissions.

Rate limiting

Rate limiting protects services and keeps fair use. Choose a strategy that fits your load and failure mode:

  • Fixed window: simple to implement, but bursts can happen at window edges.

  • Sliding window: smoother distribution, at the cost of a bit more state.

  • Token bucket or leaky bucket: steady flow with bursts allowed within a limit.

Practical tips: apply limits per API key, per user, or per IP, depending on your threat model. Store counters in a fast store like Redis and refresh quotas as tokens or bucket capacity. Return 429 Too Many Requests and include a Retry-After header so clients can retry gracefully.

Putting it into practice, set authentication at the edge, enforce authorization in the service layer, and apply rate limits at the gateway. Regularly review token lifetimes and revoke credentials when you suspect compromise.

Key Takeaways

  • Authenticate callers securely using appropriate methods for your use case.
  • Enforce precise authorization with scopes, RBAC or ABAC to follow least privilege.
  • Use robust rate limiting to protect resources and communicate clear retry guidance.