As a quality assurance expert, ensuring the security of web applications and APIs is a top priority. In this article, we'll discuss the importance of security testing and code review for web applications and APIs, and provide some best practices to follow.

Security testing is an essential part of the web application development process. It involves testing the application for vulnerabilities and weaknesses that could be exploited by attackers. Security testing should be performed throughout the development process, from the early design phase to the final testing before deployment.

Code review is another important aspect of ensuring the security of web applications and APIs. A thorough code review can identify vulnerabilities that may have been missed during the testing phase. Code review can also help identify coding practices that may be susceptible to security breaches, and can provide valuable feedback to developers on how to improve their coding skills.

When performing security testing and code review for web applications and APIs, it's important to follow best practices. These include:

1. Understand the application's architecture: Before testing or reviewing the code, it's important to understand the application's architecture and how it works. This will help identify potential vulnerabilities and weaknesses.
2. Use automated tools: Automated testing tools can help identify common vulnerabilities quickly and efficiently. However, it's important to note that they may not catch all vulnerabilities, so manual testing and code review are still necessary.
3. Review third-party libraries: Many web applications and APIs use third-party libraries, which may contain vulnerabilities that could be exploited. It's important to review these libraries and ensure they are up-to-date and secure.
4. Conduct threat modeling: Threat modeling involves identifying potential threats and attack scenarios, and designing security measures to prevent them. This can help identify vulnerabilities that may not be obvious through testing or code review.
5. Conduct regular testing and review: Security threats are constantly evolving, so it's important to conduct regular security testing and code review to identify and address new vulnerabilities.

In conclusion, security testing and code review are crucial components of ensuring the security of web applications and APIs. By following best practices and conducting regular testing and review, quality assurance experts can help ensure that web applications and APIs are secure and reliable.