REST API Security: Foundations and Best Practices

6 Best Practices for Securing REST APIs

To protect your REST APIs from cyberattacks, you need to follow API security best practices throughout their lifecycle, design, development, implementation, and decommission. Listed below are 6 API security best practices for protecting RESTFUL services.

#1. Add Authentication and Authorization to Your REST APIs

A security best practice essential for REST APIs is implementing proper API authentication and authorization processes.

• Authentication verifies that clients accessing your API have the proper access credentials and are who they appear to be.
• Authorization defines the API actions they can perform, limiting clients to only specific, approved tasks.

Without effective API authentication and authorization in place, anyone is able to make any API request they want. Exposing sensitive data and opening your API to potential abuse with malicious actors hijacking its functions for their own reasons.

There are many ways to implement REST API authentication and authorization. Most methods use either a security token or key as a unique identifier to verify the user and their level of API access. However, these approaches can introduce security concerns without encryption, as the identifier is sent with each request and can be intercepted. The best way to implement REST API authentication and authorization is to integrate security standards such as OAuth 2.0. This protocol issues short-lived access tokens for effective identity management and improved security.

REST API authentication and authorization processes can be both simplified and improved through the use of an API gateway. These tools create a single entry point for API requests, making it easier to standardize and scale REST API security processes such as authentication and authorization.

#2. Encrypt All REST API Traffic

With REST APIs sending HTTP traffic back and forth between clients and the server, encryption is a must for maintaining data integrity. Any data transferred by REST APIs is susceptible to man-in-the-middle attackers without encryption. This includes API keys and security tokens, business data, and the client’s personal information. Beyond REST API security, protecting authentication details is also fundamental to your broader web application security.

Data in transit should be encrypted using Transport Layer Security (TLS ) and data at rest using algorithms like Advanced Encryption Standard (AES). Again, encryption can be simplified with an API gateway to centralize traffic through a single entry point.

#3. Implement Throttling and Rate Limiting

A simple way REST APIs can be attacked is through sending large volumes of requests to overwhelm the server and disrupt operations. These denial-of-service attacks aim not to infiltrate your systems but to interrupt your services, stopping legitimate users from accessing them.

The best way to protect against denial-of-service attacks and maintain REST API security is throttling or rate limiting. This caps the number of requests that clients can make in a given period. With a limit in place, it is significantly harder to overwhelm servers with malicious requests. Throttling and rate limiting in REST APIs is another security process that can be implemented through API gateways.

The simplest implementation is static rate limiting in REST APIs, which places a hard limit on the number of requests during a fixed period. More sophisticated throttling algorithms take an adaptive approach, adjusting the limit based on contextual information. This includes expected usage trends, client behavior, and identifying suspicious patterns in the API traffic.

#4. Validate All User Input

Bad actors send malicious REST API requests in the hopes of finding vulnerable web services. Therefore, you should treat all requests as suspicious and validate all the attributes they contain.

Data validation in APIs and ensuring attributes (length, format, type of parameter, etc.) conform with their expected type and value is a simple method of spotting potentially harmful requests. Any requests with attributes that don’t match expectations should be sanitized or blocked.

This process of data validation in APIs and blocking suspicious requests is a critical aspect of securing RESTful services. Without it, your REST APIs can receive malicious inputs, potentially exposing your sensitive data and business logic. This includes SQL injection and cross-site scripting attacks.

A related API security best practice you should also follow is narrowly defining your REST API responses. Make it so responses are limited to a small list of approved content types to minimize the chances of abuse by cybercriminals.

#5. Implement Continuous API Discovery

As you update and deploy new web services, the number of REST APIs you utilize can quickly spiral, making it difficult to track and document your entire API ecosystem. This creates significant API security issues as you can’t secure REST APIs you aren’t aware of.

To maintain REST API security, you must implement continuous API discovery processes that collect data from a range of sources and compile a comprehensive inventory. This includes unexpected APIs, such as:

• Shadow APIs: Developed outside of normal processes and don’t necessarily follow your security protocols

• Zombie APIs:  Old or forgotten APIs that are no longer updated to remain secure.

With full visibility, you can ensure full REST API security coverage. Shadow APIs can be documented and integrated into your security procedures. Old or unmaintained zombie APIs can be properly decommissioned to ensure they can no longer be accessed for malicious purposes.

#6. Perform Regular REST API Security Testing

To protect yourself against unsecured or vulnerable REST APIs, you must regularly perform security tests and scans. This should be part of the entire API lifecycle, incorporated from development in the CI/CD pipeline through to deployment, use, and decommission, ensuring old unmaintained APIs can no longer be accessed.

Security testing includes:

• Scanning for vulnerabilities and known exploits in REST API code.
• Monitoring API traffic for threat signatures and suspicious patterns.
• Penetration testing and simulating cyberattacks to see if your REST APIs remain secure.
• Behavioral analytics to track normal REST API activity and identify anomalies.