크로스도메인 CORS 관련 레퍼런스 URL

* CORS Reference

https://developer.mozilla.org/ko/docs/Web/HTTP/CORS

https://developer.mozilla.org/ko/docs/Web/Security/Same-origin_policy

http://www.w3.org/TR/cors/

* XMLHttpRequest.open() : https://developer.mozilla.org/ko/docs/Web/API/XMLHttpRequest/open

* HTTP request methods : https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods

* HTTP 헤더 목록 참조 : https://developer.mozilla.org/ko/docs/Web/HTTP

* XMLHttpRequest.setRequestHeader() : https://developer.mozilla.org/ko/docs/Web/API/XMLHttpRequest/setRequestHeader

* Forbidden header name : https://developer.mozilla.org/en-US/docs/Glossary/Forbidden_header_name

* Forbidden response header name : https://developer.mozilla.org/en-US/docs/Glossary/Forbidden_response_header_name

* synchronous ajax error(withCredentials) : http://www.w3.org/TR/XMLHttpRequest/#the-withcredentials-attribute

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