Modern API Security Checklist

APIs are the backbone of modern software systems, enabling communication across mobile apps, SaaS platforms, and microservices. However, they also present one of the largest attack surfaces. This guide offers a current, comprehensive checklist to help you secure your APIs against today's most common and impactful threats.

1. Use Strong and Standardized Authentication

Implement OAuth 2.0 with OpenID Connect for user authentication and authorization
Use mutual TLS (mTLS) or signed tokens for internal service communication
Use trusted platforms like Auth0, Keycloak, or AWS Cognito

2. Encrypt All Data in Transit and at Rest

Enforce HTTPS using TLS 1.3 or higher across all environments
Encrypt data at rest using KMS or secure disk encryption
Use HSTS headers and consider certificate pinning for mobile clients

3. Apply Proper Authorization Logic

Use RBAC or ABAC models to restrict resource access
Validate user roles and ownership server-side
Use opaque, non-sequential identifiers to prevent IDOR vulnerabilities

4. Use an API Gateway or Service Mesh

Deploy an API gateway (e.g. Kong, Apigee, Traefik) to enforce security controls centrally
Use service meshes like Istio for policy enforcement and observability
Apply geofencing, IP whitelisting, and request filtering at the edge

5. Rate Limiting and Abuse Detection

Implement rate limits and burst controls per user and IP
Throttle or block abusive clients automatically
Monitor for scraping, credential stuffing, and DDoS activity

6. Input Validation and Schema Enforcement

Validate input types, lengths, and formats at the edge and in the app
Use OpenAPI or GraphQL schema validation to enforce contracts
Sanitize inputs to prevent SQL, NoSQL, and command injection

7. Harden HTTP Behavior

Disable unused HTTP methods (e.g. PUT, DELETE) when not needed
Return correct Content-Type headers and reject unexpected formats
Avoid leaking sensitive details in error messages or stack traces

8. Monitor and Log Security-Relevant Events

Log authentication attempts, permission errors, and sensitive operations
Use centralized logging platforms like ELK or Datadog
Integrate with SIEM tools for correlation and threat detection

9. Shift Security Left in CI/CD

Use SAST and DAST tools in your development pipeline
Scan dependencies with tools like Snyk, Dependabot, or Trivy
Monitor for third-party vulnerabilities

10. Follow OWASP API Security Top 10

Protect against Broken Object Level Authorization
Avoid excessive data exposure and lack of rate limiting
Keep documentation updated and remove deprecated endpoints

BONUS: Enforce Privacy and Compliance

Implement data retention and deletion workflows
Do not log sensitive data such as tokens or passwords in plaintext

BONUS: Use API-Specific Threat Detection

Leverage tools that detect behavioral anomalies in API usage
Correlate traffic patterns to identify and block abuse in real time

API security is a continuously evolving discipline. This checklist helps you enforce the basics while adopting modern practices that address today's attack surface. Start with authentication, encryption, and authorization, then layer on monitoring, validation, automation, and compliance controls. Secure APIs are not just a technical necessity, they are foundational to customer trust and business resilience.