Overview

Every API needs proper security controls.

Step 1: Authentication

Authorised access only.

1

Methods

API Keys for basic use
OAuth 2.0 for delegated access
JWT for stateless auth
Always HTTPS

2

Tokens

Short expiry: 15-60 minutes
Validate on every request
Implement revocation

Step 2: Protection

Defend against attacks.

1

Rate Limiting

100 req/min standard
10/min for auth endpoints
429 response when exceeded

2

Validation

Validate ALL input
Enforce types and lengths
Parameterised queries
Request size limits

Step 3: Monitoring

Detect abuse.

1

Practices

Log all requests
Monitor patterns
Alert on failures
Regular security testing

3

API Security Headers

Set Content-Type headers explicitly on all responses
Add X-Content-Type-Options: nosniff to prevent MIME type sniffing
Set X-Frame-Options: DENY to prevent clickjacking
Configure CORS (Cross-Origin Resource Sharing) to allow only trusted domains
Add Cache-Control: no-store for sensitive API responses
Set Strict-Transport-Security header to enforce HTTPS
Remove server version headers that reveal technology stack information

4

API Versioning and Documentation

Version your API from day one: /api/v1/, /api/v2/
Maintain backward compatibility or provide migration guides
Keep API documentation private, do not expose to unauthenticated users
Use OpenAPI/Swagger for structured API documentation
Document rate limits, authentication requirements, and error codes
Review documentation accuracy with every API release

5

API Penetration Testing

Test against the OWASP API Security Top 10 vulnerabilities
Test for: Broken Object Level Authorisation (can user A access user B's data?)
Test for: Mass Assignment (can clients set fields they should not?)
Test for: Excessive Data Exposure (does the API return more data than needed?)
Use tools: Burp Suite, OWASP ZAP, Postman for security testing
Schedule API security testing before major releases and annually
Include API endpoints in your regular penetration testing scope

Pro Tip:

The most common API vulnerability is Broken Object Level Authorisation, where changing an ID in the URL lets you access another user's data. Test every endpoint with different user roles.

Overview

Step 1: Authentication

Methods

Tokens

Step 2: Protection

Rate Limiting

Validation

Step 3: Monitoring

Practices

API Security Headers

API Versioning and Documentation

API Penetration Testing

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