𝗪𝗵𝘆 𝗗𝗲𝘃𝗲𝗹𝗼𝗽𝗲𝗿𝘀 𝗗𝗼𝗻'𝘁 𝗨𝗻𝗱𝗲𝗿𝘀𝘁𝗮𝗻𝗱 𝗖𝗢𝗥𝗦

𝗪𝗵𝘆 𝗗𝗲𝘃𝗲𝗹𝗼𝗽𝗲𝗿𝘀 𝗗𝗼𝗻'𝘁 𝗨𝗻𝗱𝗲𝗿𝘀𝘁𝗮𝗻𝗱 𝗖𝗢𝗥𝗦

CORS is one of the most misunderstood security tools in web development. Many developers think it protects their server. It does not.

CORS protects the user.

The browser enforces the Same-Origin Policy (SOP). This policy stops a malicious site from making requests to another site on your behalf. CORS is simply the way a server tells the browser to relax that rule for specific sites.

If your request works in Postman but fails in a browser, you have a CORS issue. Postman is not a browser, so it does not enforce these rules.

Common mistakes you must avoid:

• Using CORS as your only security. CORS is not authentication. You still need tokens, passwords, and rate limiting.
• The wildcard trap. You cannot use Access-Control-Allow-Origin: * if you need to send cookies or credentials. You must list the exact domain.
• Ignoring preflight requests. Browsers send an automatic OPTIONS request before many API calls. If your server blocks OPTIONS, your actual request will fail.
• Missing error headers. If your API returns a 401 or 500 error without CORS headers, the browser hides the real error. You will only see a generic CORS message.

How to fix it:

• Handle OPTIONS requests. Ensure your server returns a 200 or 204 status for preflight calls.
• Use middleware. Configure CORS at the middleware level to ensure it covers all responses, including errors.
• Set the Vary header. If you allow multiple origins dynamically, you must add Vary: Origin to your response.
• Use the right tools. For Node.js, use the cors package. For Django, use django-cors-headers.

Stop trying to bypass CORS with browser extensions. Fix your server configuration instead.

Source: https://dev.to/onsen/why-developers-dont-understand-cors-and-how-to-fix-it-19d5

Optional learning community: https://t.me/GyaanSetuAi