Umesh

Dec 20, 2024

Breaking Down CORS: Getting the Hang of Cross-Origin Requests in Web Development

Cross-Origin Resource Sharing or CORS is a security feature implemented in web browsers that allows controlled access to resources hosted on a different domain.

It's a handy feature that helps developers by making safe and controlled communication between web applications on different origins or domains while mitigating potential security risks.

Before CORS, the same-origin policy was used to restrict web pages from making requests to domains other than their own. This was a security measure to prevent unauthorized data access and potential malicious actions. CORS introduced a mechanism that involves both the browser and the server to allow controlled cross-origin requests.

CORS is a significant advancement in web development, simplifying the process of integrating and interacting with resources hosted on different domains. It allows developers to create more feature-rich applications by leveraging external data and services, all while maintaining a strong focus on security and controlled access. ⁠

Alright, let’s check out how CORS works, how requests get sent, and how the server sends back the response.

When a web page makes a cross-origin request, it may be an XMLHttpRequest or Fetch request, the browser adds an Origin header to the request including the requested domain.

The server receives the request and responds with specific CORS-related headers. Based on the Origin header the server can allow or deny the request. If the server permits it, it sends back a response with the requested data, if not, the browser blocks the request.

It enables us to retrieve data from different domains while adhering to security best practices. This is essential for integrating third-party APIs or fetching resources from external services. ⁠It allows us to send requests for data from different websites directly using JavaScript on the user's browser. There's no need to set up extra server helpers or use complicated methods to get around restrictions. This makes the code simpler and the overall structure of the application easier to manage.

As it is set up in a standard way that most browsers follow, we can expect similar results no matter which browser users are browsing from. Server-side configuration lets developers decide which websites can use certain resources, like data or files, from their server.

By combining accessibility with robust security measures, it finds a way to make things easy to access while also keeping them safe. This mix of being user-friendly and secure is important for creating websites today.