CORS preflight: Definition, Use Cases, and Examples
TL;DR:
CORS preflight is an OPTIONS request that the browser sends before a "complex" cross-origin request (non-standard headers, PUT/DELETE methods). The server must respond 200 with Access-Control-Allow-Methods / Headers. If preflight fails, the main request is not sent. Common cause of "CORS errors" in the browser console.
What is CORS preflight
CORS preflight is an OPTIONS request that the browser sends before a "complex" cross-origin request (non-standard headers, PUT/DELETE methods). The server must respond 200 with Access-Control-Allow-Methods / Headers. If preflight fails, the main request is not sent. Common cause of "CORS errors" in the browser console.
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Frequently Asked Questions
Do I need CORS preflight?
See the use-case section above. For a quick check, use our online form.