How To Guide
How to Secure API Endpoints for Applications
APIs without security are an open door to your data.
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.
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