This is a request header that is used when issuing a preflight request so as to let the server know which HTTP method would be used when the actual request is made. This header is of importance as the preflight request is always an OPTIONS (a HTTP method that is used to describe the communication options available for the target resource) and also it does not use the same method as the actual request.
This header signifies a specific HTTP method of the actual request. It is always incorporated, even though the HTTP method under consideration is just a simple HTTP method as mentioned before (such as, GET, POST, and HEAD).
This request header is provided or set by browser on the CORS preflight requests. It is said to hold just a single value.
Enablement in Apache:
The below given syntax is added in the configuration file.
Header set Access-Control-Request-Method “PUT”
Enablement in Nginx:
The syntax given below is added in the “nginx.conf” file.
add_header ‘Access-Control-Request-Method’ ‘ PUT ‘;