CORS : Cross Origin Resource Sharing

Cross-Origin Resource Sharing (CORS) is a browser mechanism that allows controlled access to resources located outside of a given domain. It's a security feature that helps prevent malicious scripts from accessing sensitive data on other domains.

Here's a breakdown of CORS:

What it does:

• Enables controlled sharing of resources between different domains.

• Protects sensitive data from unauthorized access.

• Defines how a browser and server can interact to allow or deny cross-origin requests.

How it works:

1. A web application from one domain (origin) makes a request to a resource on another domain (target).

2. The target server checks its CORS configuration to see if the request is allowed.

3. If the request is allowed, the server sends a response back to the origin.

4. If the request is denied, the browser will block the request and prevent the application from accessing the resource.

CORS headers:

• Access-Control-Allow-Origin: Specifies which origins are allowed to access the resource.

• Access-Control-Allow-Methods: Specifies which HTTP methods are allowed to be used for requests (e.g., GET, POST, PUT, DELETE).

• Access-Control-Allow-Headers: Specifies which HTTP headers are allowed to be sent with the request.

• Access-Control-Allow-Credentials: Specifies whether cookies and other HTTP credentials can be sent with the request.

Benefits of CORS:

• Improved security by restricting access to sensitive data.

• Enables development of complex web applications that rely on resources from other domains.

• Provides a standardized way for browsers and servers to communicate about cross-origin requests.

Examples of CORS in action:

• When you embed an image from another website on your blog.

• When you use a social media plugin to share content from another website.

• When you use an API to access data from another website.

Resources for further learning:

• MDN Web Docs: https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS

• Wikipedia: https://en.wikipedia.org/wiki/Cross-origin_resource_sharing

• AWS: https://docs.aws.amazon.com/AmazonS3/latest/userguide/cors.html