About HTTP Headers

The following table provides information about some of the HTTP headers used in requests and responses.

Header	Type	Definition
Access-Control-Request-Method	Request	Used by browsers when issuing a pre-flight request inform the server which HTTP method will be used when the actual request is made.
Origin	Request	Identifies the URL from which the request originated.
Access-Control-Request-Headers	Request	Used by browsers when issuing a pre-flight request to inform the server which HTTP headers the client intends to send in the actual request. The server’s response to this header is the Access\-Control\-Allowed\-Headers header, informing the client which headers are allowed in the request.
Access-Control-Allow-Origin	Response	Indicates that the origin of the request can access the response. If the origin is not permitted to send the request, a 403 code is returned for a pre-flight request, while an actual request fails with a CORS error.