In a scenario involving legacy systems and strict data integrity requirements, SOAP is a viable choice. SOAP provides a well-defined and structured way to ensure data integrity, making it suitable for such scenarios, even though it might be less lightweight than other styles.

Unit testing is a type of API testing that focuses on verifying that individual components or functions of an application work as expected in isolation. It involves testing each component in isolation to ensure that it performs its specific functions correctly. Unit testing is an essential part of API testing to validate the smallest building blocks of an application.

In Express, the app.use() function is used to add "middleware" that can process incoming requests before they reach the routes. Middleware functions can perform tasks like authentication, logging, or modifying request/response objects.

API monitoring and analytics can help identify and prevent security breaches by detecting unauthorized access patterns. By analyzing historical API usage data, patterns of unusual or suspicious behavior can be spotted, indicating potential security breaches. While detecting vulnerabilities in the code and encrypting data are important security measures, monitoring is essential for identifying and reacting to real-time security threats.

To protect against CSRF (Cross-Site Request Forgery) attacks, developers can implement Cross-origin resource sharing (CORS) to ensure that requests are only accepted from trusted sources. CORS helps prevent unauthorized websites from making malicious requests to APIs on behalf of users.

To handle CORS issues in APIs created with Node.js and Express, you should configure CORS middleware. This middleware allows you to specify the allowed origins, HTTP methods, and headers for incoming requests. Automatically handling CORS is not the default behavior, and disallowing all cross-origin requests is not a practical solution. Using a third-party API gateway may be an option but is not the primary method for handling CORS.

CSRF (Cross-Site Request Forgery) can allow attackers to perform actions on behalf of authenticated users. To mitigate this risk, you should explain the potential dangers to the development team. Mitigate by implementing anti-CSRF tokens, using the SameSite attribute in cookies, and validating the origin of requests. These measures help protect against CSRF attacks.

Fine-tuning the granularity of API throttling can ensure that resources are not overused while still providing a responsive service. Granularity refers to the level of detail at which you set throttling limits. By defining specific limits for different types of requests, you can optimize resource allocation.

ASP.NET Core is primarily used for building server-side web applications. It's a cross-platform, high-performance framework that enables developers to create robust, scalable, and efficient web applications that can run on Windows, Linux, and macOS. It's not focused on client-side JavaScript, mobile app development, or database management.

API key rotation is a practice where API keys are periodically regenerated to enhance security. This process involves generating new API keys to replace the old ones, reducing the risk of unauthorized access and misuse of keys. It's a vital security measure to protect APIs.