What is cross-origin resource sharing (CORS)?

Cross-origin resource sharing (CORS) is fundamentally a security feature introduced to protect users and their data on the web. It specifically addresses the same-origin policy, which is a web security measure that prevents scripts running on one origin (protocol, domain, and port) from making requests to another origin. Without CORS, a web application could potentially be exploited by malicious scripts from other origins, compromising user information or making unauthorized requests.

CORS allows servers to specify who can access their resources and under what conditions. By implementing CORS, a server can grant permission to specific origins to access its resources through HTTP headers. This controlled access is essential for modern web applications that often need to request resources from different domains, such as APIs or assets hosted elsewhere.

This concept is crucial for maintaining the security and integrity of web applications while enabling interoperability across different domains, which is increasingly important in today's distributed web architecture.