Guide to Developing Secure APIs

APIs have become extremely important and will continue to gain even more importance with time. The reason being as more and more companies are shifting to cloud solutions and micro-service architecture, it becomes crucial to enable communication between applications and services over the network.

Different kinds of APIs are used depending upon the use case, the most common one being REST APIs for web applications, although other alternatives exists such as GraphQL and gRPC. Regardless of the API style you chose this guide will give you a checklist that your API must satisfy to qualify as a secure API. Let’s get started.

Use HTTPS

The first step to securing your API is encrypting all traffic between the client and the server. Using HTTPS instead of HTTP ensures that data in transit is encrypted with SSL/TLS, protecting sensitive information like login credentials, API keys, and personal data from being intercepted by attackers. Always enforce HTTPS on your API endpoints to maintain confidentiality and integrity. You can check out how to quickly set up HTTPS connection on Apache servers in my previous post

Use OAuth2 for authentication

OAuth2 is a robust framework for managing secure authentication in your API. By using OAuth2, you can delegate authentication to trusted identity providers like Google, Facebook, or your own system. OAuth2 allows users to authenticate without sharing their passwords directly, improving security. It also supports token-based authentication, which simplifies managing user sessions and revoking access when necessary. This eliminates the user to create complex passwords and risk forgetting them. If you wish to know more about OAuth2, you can check this post on DigitalOcean.

Implement WebAuthn for Passwordless Security

WebAuthn is a modern, secure, and passwordless authentication standard that leverages biometric data or hardware keys for authentication. By supporting WebAuthn, you can provide users with a secure way to access your API without relying on passwords, which are often vulnerable to brute-force attacks and phishing. This method ensures high-level security and improves user experience.

Here is a demo of how WebAuth works

Leveled API Keys for Granular Access Control

Leveled API keys allow you to assign different permission levels to API users. For example, a read-only key might be used by clients that only need to view data, while a higher-privileged key might allow data modification. This ensures that users only have the access necessary for their role, minimizing the damage that can be done in case of a key compromise. Regularly rotate and revoke unused keys to enhance security further.

Authorization

Implement Role-Based Access Control (RBAC) to enforce granular permissions based on user roles. This prevents unauthorized users from accessing sensitive endpoints or performing restricted actions, reducing the risk of data breaches.

Rate Limiting

To protect your API from Denial of Service (DoS) and brute-force attacks, implement rate limiting. By setting a cap on the number of requests that a user can make within a specific time frame, you can prevent misuse and overload of your services. Rate limiting also ensures fair usage of resources and helps maintain performance for all users.

API Versioning

As your API evolves, versioning becomes essential to ensure backward compatibility and secure changes. With proper versioning, you can introduce new features, deprecate insecure endpoints, and update security protocols without breaking client integrations. Using URL-based versioning, for example, /v1/resource is a common and effective method to manage API versions.

Allow Listing

Using an allow list is a security best practice that limits access to your API to only trusted sources. By default, deny access to everyone except clients explicitly permitted. This approach helps mitigate unauthorized access from unknown or untrusted sources, especially when combined with API keys and authentication.

Use an API Gateway

An API gateway acts as a single entry point for all API requests and enforces security policies across all endpoints. It can manage authentication, rate limiting, and request validation while also providing features like load balancing, caching, and logging. Using an API gateway simplifies the management of complex APIs and strengthens security by centralizing access control.

Verbose Error Handling

Error handling is crucial for debugging, but improper error messages can leak sensitive information, such as internal server structures or API keys. Implement verbose error handling, but ensure that any information shared with the client is limited to what is necessary. For example, avoid revealing stack traces or database details in production environments. Instead, provide general messages like “Invalid request” while logging full details for internal review.

Example of a bad error handling

In the above example this a error page of a django application.

This above example is how a request should be handled

Validate Input

Input validation is one of the most effective ways to secure your API against common vulnerabilities like SQL injection, cross-site scripting (XSS), and command injection. By validating and sanitizing all incoming data, you prevent attackers from injecting malicious code or unauthorized queries. Validate both data types and formats (e.g., email, URL, phone numbers) to ensure only expected values are processed.

Conclusion

Security is an ongoing process, so always review and update your API security practices to stay ahead of evolving threats. Following these strategies will not only improve your API’s security but also foster confidence among your users and partners.

Always ensure your APIs are cross-verified against the OWASP API Security Project. This widely respected framework identifies the top security vulnerabilities specific to APIs, such as broken authentication, improper data handling, and injection attacks. By regularly auditing your APIs against these best practices, you can mitigate risks and strengthen your security posture