How CORS Works

Routify is a serverless API Gateway that allows you to build, deploy, and manage APIs with ease. It is designed to be simple to use and easy to understand, so you can focus on building great APIs without worrying about the infrastructure.

One of the features that Routify provides is CORS (Cross-Origin Resource Sharing) support.

In the modern web development landscape, Cross-Origin Resource Sharing (CORS) is a critical concept that enables websites to safely and securely access resources from a server on a different domain than the one the website was served from. Understanding CORS is essential for developers working with APIs, external media, and cross-domain scripts. Here’s a straightforward explanation of how CORS works and why it's important.

What is CORS?

CORS is a security feature implemented by web browsers to prevent potentially malicious websites from accessing sensitive data on another domain without permission. Before CORS was implemented, scripts on webpages could only make requests to the same domain from which the original page was loaded. This policy, known as the "Same-Origin Policy," helps to safeguard user data against various web-based threats.

How CORS Works

The process of CORS operates through HTTP headers to tell the browser to allow web applications running at one origin (domain) to gain permission to access selected resources from a server at a different origin. Here is a simple step-by-step breakdown:

• The Browser Makes a Preflight Request: When a web application tries to fetch resources from a different domain, the browser sends an HTTP OPTIONS request to the server as a "preflight" to check if the CORS policy allows the actual request. This preflight isn't needed for all requests but is used for requests that can potentially modify data (like HTTP methods PUT, DELETE, POST, etc.).

• Server Response: The server responds to the preflight request with the appropriate CORS headers. These headers include statements about which domains are allowed (with Access-Control-Allow-Origin), which HTTP methods are permitted (Access-Control-Allow-Methods), and other details about what the requesting domain can do.

• Actual Request: If the server's response allows the cross-origin request, the browser then sends the actual request to the server to access the resources needed.

• Resource Sharing: If all the CORS policies are met, the server will respond with the requested resource, also including CORS headers in the response to ensure that everything is allowed as per the policy.

Why is CORS Important?

CORS helps maintain the security integrity of the web while still allowing controlled, resource-sharing between different domains. This is particularly important in a cloud-based, service-oriented architecture where integrating different services and APIs is a common requirement.

• Security: By implementing CORS, servers can keep their resources secure while making them accessible to authorized domains.
• Flexibility: CORS enables companies to access resources across different platforms securely and efficiently, which can lead to better integration of web services and richer user experiences.
• Control: Server administrators have precise control over how and when their resources are accessed from other domains through the use of specific CORS policies.