7 Best Practices for Secure API Development

According to Traceable, 60% of organisations reported that they experienced a data breach in the past two years. Of these breaches, 74% encountered at least three API-related breaches.?

These stats simply say, “We need to build more secure APIs”!

An API that exposes user data without authentication can leave sensitive information vulnerable to anyone who accesses it. Compare that to an API using token-based authentication, where only verified users can access data, and all transmissions are encrypted. The difference is clear.

API development involves building the connections that allow different software systems to communicate. It’s essential in today’s software ecosystem, but with this openness comes risk. Secure API development protects user data, prevents unauthorised access, and keeps services reliable.

From my 11+ years as a developer, I have compiled seven proven best practices for building secure APIs.?

1. Use HTTPS to Encrypt Data in Transit

Every API should use HTTPS to secure data exchanged between clients and servers. HTTPS (Hypertext Transfer Protocol Secure) encrypts transmitted data, blocking attackers from intercepting or modifying it. This is especially important for APIs handling sensitive information like user details or payment data.

For example, Stripe, a popular payment gateway uses HTTPS across its APIs to protect transactions. Without HTTPS, attackers could exploit vulnerabilities with a man-in-the-middle (MITM) attack and gain access to sensitive information.

Another example is Twitter’s API (now X). It secures sensitive data such as user authentication details and direct messages with HTTPS. Similarly, GitHub’s API implements HTTPS to secure interactions like repository management and code pushes.

HTTPS ensures that OAuth tokens and other sensitive information remain encrypted during transmission.

2. Strong Authentication and Authorization

Your API must recognise that not all users should have the same level of access. Authentication verifies users' identities, while authorisation dictates what each user can do within the system.?

A widely used approach for authentication is OAuth 2.0. It allows users to get applications access without sharing their passwords. For instance, many social media platforms use OAuth 2.0 to let users log into third-party apps with their Google or Facebook accounts to maintain user privacy and seamless integration.

However, you cannot rely solely on OAuth 2.0. You should strengthen your security with multi-factor authentication (MFA), such as a one-time code sent to the user’s phone or an authentication app. This makes it harder for attackers to gain access, even if they’ve obtained the login credentials.

Additionally, you should apply role-based access control (RBAC) to limit access to certain endpoints based on user roles. Only users with the appropriate permissions should be able to access or modify sensitive data.?

For example, a finance API might grant read access to general users for account balances while restricting write access to only admin-level users for tasks like adjusting credit limits.

3. Validate and Sanitise Inputs to Prevent Injection Attacks

Without proper input validation, APIs are vulnerable to injection attacks like SQL injection. This risk is especially high for APIs interacting with databases.?

Input validation ensures that the data received matches expected formats, while sanitization removes or neutralises potentially harmful characters.

Let's use an API that processes user-generated data, such as a search query. An attacker could attempt to inject malicious SQL code into this input to gain unauthorised access to your database. To prevent this, you can enforce strict input rules using validation libraries like OWASP’s API Security Project.?

For instance, if your API accepts a user’s age, validation should confirm that it’s a number within a defined range. At the same time, sanitisation removes any special characters that could be used for attacks.

Aside from basic input checks, parameterised queries and prepared statements can further protect your API against injection attacks by ensuring that user inputs are treated as data rather than executable code. This combination of input validation, sanitization, and secure database queries reduces the risk of code injection.

4. Rate Limiting and Throttling to Prevent DDoS Attacks

Even the most secure APIs can fall victim to Distributed Denial of Service (DDoS) attacks, where an attacker floods the API with requests to exhaust server resources. Rate limiting and throttling are essential defences that let you restrict how many requests a client can make in a set time period.

For instance, GitHub’s API applies rate limits on the number of requests a GitHub App can make to the REST API within a specific period. By capping requests, you prevent your servers from being overwhelmed.?

Throttling takes this a step further by slowing down responses as a user approaches their limit. In other words, you gently curb abuse without outright blocking legitimate users.

5. Use an API Gateway for Centralized Security

An API gateway acts as a security checkpoint that manages and controls all your API traffic. It provides a central point for authentication, rate limiting, and logging.?

For example, Amazon API Gateway lets you set up access controls, monitor usage, and manage API keys. Other options include Kong, Apigee, and Azure API Management.

With an API gateway, you ensure all your API endpoints follow the same security rules without constant manual checks. Centralised approach like this strengthens your overall API security while reducing the complexity of managing multiple endpoints.

6. Monitor and Log API Activity to Detect Suspicious Behavior

Continuous monitoring will help you to identify and respond to suspicious activity. Implement logging for all API calls, including timestamps, user details, and IP addresses.?

I recommend tools like ELK Stack (Elasticsearch, Logstash, and Kibana) to help you track API usage patterns and identify anomalies.

For instance, if you notice a sudden spike in API requests from a single IP address, it could be a sign of an attempted DDoS attack or brute-force login attempts. Monitoring allows you to take proactive measures, such as blocking IPs or temporarily suspending suspicious accounts.

7. Keep APIs Updated and Patch Vulnerabilities

Do you remember the Heartbleed bug that occurred in 2014? An unpatched OpenSSL vulnerability that affected millions of servers worldwide. Those who quickly updated their systems minimized the risk.?

Security is never a set-and-forget task—vulnerabilities evolve, and so must your API. Regularly update your API software, libraries, and dependencies to address known security issues.?

Software like Dependabot can automatically notify you when dependencies need updating, so you can always run the latest, most secure versions. Prioritising patches and updates will help you shield your API from potential exploits.

Wrapping Up

So, those are my seven infallible tricks for building Secure APIs!

With these seven practices, you will protect your digital assets and gain the confidence that comes from knowing you’ve covered all your bases.

Overall, secure API development requires a strategic approach, where every layer of security plays a role in protecting your data and users. From encrypting data with HTTPS to monitoring for unusual activity, each best practice helps build a resilient API that can withstand today’s cyber threats.?