APIs are the most common attack vector in modern application security. The OWASP API Security Top 10 documents the most critical API vulnerabilities, and the list grows longer each year as APIs proliferate. Securing your APIs is not optional — it is a fundamental requirement for any business that handles customer data.
The OWASP API Security Top 10
The Open Web Application Security Project (OWASP) maintains a list of the most critical API security risks. Understanding these risks is the foundation of API security.
| Risk | Description | Prevention |
|---|---|---|
| Broken Object Level Authorization | API returns data for any object ID | Validate user owns the requested object |
| Broken Authentication | Weak or missing authentication | Implement OAuth 2.0 + JWT properly |
| Excessive Data Exposure | API returns more data than needed | Return only required fields |
| Lack of Rate Limiting | No limits on API request volume | Implement rate limiting per user/IP |
| Broken Function Level Authorization | Users can access admin functions | Separate admin and user API surfaces |
| Mass Assignment | API accepts all input fields | Whitelist allowed input fields explicitly |
| Security Misconfiguration | Default settings left in place | Security-focused configuration review |
| Injection | SQL/NoSQL injection via API inputs | Parameterized queries, input validation |
Authentication and Authorization
OAuth 2.0 and JWT
OAuth 2.0 is the industry standard for API authorization. JSON Web Tokens (JWT) are the standard format for access tokens. Implement short-lived access tokens (15-60 minutes) with refresh token rotation. Never store tokens in localStorage — use httpOnly cookies for web applications.
API Keys for Service-to-Service
For server-to-server API calls, API keys are simpler than OAuth. Store API keys in environment variables or secrets management services (AWS Secrets Manager, HashiCorp Vault). Rotate API keys regularly and immediately upon suspected compromise.
Scope-Based Authorization
Define granular scopes that limit what each API token can do. A token for reading user profiles should not be able to delete users. Implement the principle of least privilege — grant only the permissions required for the specific use case.
Rate Limiting and Throttling
Rate limiting prevents abuse, protects against denial-of-service attacks, and ensures fair resource allocation. Implement rate limits at multiple levels: per IP address, per API key, per user, and per endpoint. Return 429 Too Many Requests with a Retry-After header when limits are exceeded.
For business APIs, tiered rate limits based on subscription level are common: free tier (100 requests/hour), standard tier (1,000 requests/hour), enterprise tier (unlimited with fair use policy).
API Gateway as a Security Layer
An API gateway (AWS API Gateway, Kong, Apigee) centralizes security enforcement across all your APIs. Rather than implementing authentication, rate limiting, and logging in every service, the gateway handles these concerns once for all traffic. This reduces the attack surface and ensures consistent security policy enforcement.
Frequently Asked Questions
Broken Object Level Authorization (BOLA) — also called Insecure Direct Object Reference (IDOR) — is the most common API vulnerability. It occurs when an API returns data for any object ID without verifying the requesting user has permission to access that object. Always validate that the authenticated user owns or has permission to access the requested resource.
For public APIs: require API key authentication for all requests, implement rate limiting to prevent abuse, use HTTPS exclusively, validate and sanitize all inputs, return only the data the consumer needs, log all API access for audit purposes, and implement an API gateway to centralize security enforcement.
JWTs are stateless — the server does not need to store session state, making them ideal for distributed systems and microservices. Session tokens require server-side session storage but are easier to revoke immediately. For most web applications, JWTs with short expiry times (15-60 minutes) and refresh token rotation provide the right balance of security and scalability.
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