CORS
HARSH MISHRA
Software Development Engineer at SECUREU || Former SDE Intern at Kickdrum India || Teaching Assistant at Apna College || Full Stack Developer || Learning
CORS?? Demystifying CORS: A Key Element of Web Security ??
Ever wondered how Cross-Origin Resource Sharing (CORS) works? ?? It's a crucial aspect of web security that ensures safe data sharing between different domains. Let's dive into the details:
1?? Initiation of a request from a web page
It all begins when a web page (origin A) attempts to access a resource from a different origin (origin B).
2?? "Simple" or "non-simple" request check
Before proceeding, the browser checks if the request is "simple" or "non-simple." "Simple" requests include methods like GET, POST, or HEAD with a limited set of headers. For "non-simple" requests, a preflight request is initiated.
3?? Preflight request (for non-simple requests)
In the case of "non-simple" requests, the browser sends an OPTIONS request to the target origin (origin B). This request includes headers detailing the intended actual request.
4?? Server response to preflight request
Origin B's server responds to the preflight request. If it permits access, it sends headers confirming so. The browser rejects the actual request if the server doesn't provide the required headers or if they don't match the request details.
5?? The actual request is sent
With the preflight checks complete, the browser makes the actual request to origin B, including necessary headers, credentials, or data.
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6?? Server response to the actual request
Origin B's server processes the request and responds, still including relevant CORS-related headers.
7?? Browser enforcement
Finally, the browser rechecks CORS headers in the response. If all is well, it delivers the response to the web page's JavaScript. If not, it blocks access and logs a CORS error.
CORS empowers servers to control resource access, with browsers safeguarding users from potential security risks. Though CORS adds complexity, it's a vital security measure ensuring secure cross-origin data sharing.
?? Explore a real-world CORS implementation in my project: "Chat Application." With Node.js and Socket.io.
Check it out here:
Share your thoughts and experiences with CORS in the comments below! ??
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