Http Preflight Request

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When dealing with CORS the browser or front-end sends a pre-flight request to check if the CORS request is understood

From the MDN docs

A CORS preflight request is a CORS request that checks to see if the CORS protocol is understood and a server is aware using specific methods and headers.

OPTIONS /resource/foo 
Access-Control-Request-Method: DELETE 
Access-Control-Request-Headers: origin, x-requested-with
Origin: https://foo.bar.org

References