TL;DR
This guide covers essential steps to build a relatively simple but secure API for your clients. We’ll focus on authentication, input validation, rate limiting, and basic error handling.
1. Authentication & Authorisation
How do you know who is using your API? Authentication verifies identity; authorisation determines what they can access.
- API Keys: A simple starting point. Generate a unique key for each client. Store these securely (see section 5).
- Include the API Key in every request, typically as an HTTP header (e.g.,
X-API-Key) or query parameter. -
curl -H "X-API-Key: YOUR_API_KEY" https://your-api.com/data - Consider OAuth 2.0: For more complex scenarios (user accounts, delegated access), OAuth 2.0 is a better choice. It's more secure and flexible but requires more setup.
- Never store passwords directly: Use strong hashing algorithms like bcrypt or Argon2.
2. Input Validation
Don’t trust user input! Always validate everything before processing it to prevent attacks like SQL injection and cross-site scripting (XSS).
- Whitelisting: Define what is *allowed* rather than trying to block bad things.
- Data Types: Ensure data matches the expected type (e.g., integer, string, email address).
- Length Restrictions: Limit input lengths to prevent buffer overflows and denial-of-service attacks.
- Regular Expressions: Use regex for complex patterns like email validation or phone numbers.
- Example (Python):
import re if re.match(r"^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+.[a-zA-Z]{2,}$"; email): # Valid email address else: # Invalid email address
3. Rate Limiting
Protect your API from abuse by limiting the number of requests a client can make within a certain timeframe.
- Identify Clients: Use IP address, API key, or user ID to track request rates.
- Set Limits: Define appropriate limits based on your API's resources and expected usage (e.g., 100 requests per hour).
- Return Error Codes: Respond with a
429 Too Many Requestserror when the limit is exceeded. Include information about how long to wait before retrying. - Example (using a simple in-memory counter):
# Pseudo code if client_requests[client_id] > MAX_REQUESTS_PER_HOUR: return 429, "Too Many Requests" else: client_requests[client_id] += 1
4. Error Handling
Provide informative and helpful error messages to clients without revealing sensitive information.
- Generic Error Messages: Avoid exposing internal details about your system.
- HTTP Status Codes: Use appropriate status codes (e.g.,
400 Bad Request,401 Unauthorized,500 Internal Server Error). - Logging: Log errors on the server-side for debugging and monitoring purposes.
5. Secure Storage
Protect sensitive data like API keys and user credentials.
- Encryption: Encrypt all sensitive data at rest and in transit (using HTTPS/TLS).
- Environment Variables: Store API keys in environment variables, not directly in your code.
- Database Security: Use strong passwords, restrict database access, and regularly back up your data.
6. Monitoring & Logging
Keep an eye on your API's performance and security.
- Log all requests: Include timestamps, client IP addresses, endpoints accessed, and request/response details (without sensitive data).
- Monitor for unusual activity: Look for spikes in traffic, failed authentication attempts, or unexpected errors.
- Alerting: Set up alerts to notify you of potential security issues.