Access-Control-Request-Method is an integral part of the HTTP headers that enable the Cross-Origin Resource Sharing (CORS) mechanism. This header is used by the browser in a preflight request to inform the server about the HTTP method that will be used in the actual request.
What is Access-Control-Request-Method?
Access-Control-Request-Method is an HTTP request header utilized in a preflight request to let the server know which HTTP method will be used when the actual request is made. The server then responds with whether it accepts requests with this method from the origin in question.
The header follows the format:
<method> is the HTTP method (such as
DELETE, etc.) that will be used in the actual request.
For example, consider a preflight request with this header:
Here, the client is indicating that it will make the actual request with the
Scenario 1: Requesting to Use the POST Method
Suppose your client needs to make a POST request to your server. The preflight request from the client would include:
The server should then respond with an
Access-Control-Allow-Methods header containing
POST to indicate that this method is allowed:
Scenario 2: Requesting to Use the PUT Method
If your client needs to make a PUT request to your server, the preflight request would include:
The server would then respond with:
Considerations and Caveats
When working with
Access-Control-Request-Method, remember the following points:
- Server Responsibility: It’s the server’s responsibility to decide whether to allow or disallow the method specified in
Access-Control-Request-Method. If the server doesn’t respond with an
Access-Control-Allow-Methodsheader that includes the requested method, the actual request will not be allowed.
- Preflight Requests:
Access-Control-Request-Methodis used in preflight requests. These requests are sent automatically by the browser under certain conditions to check the server’s CORS policy before making the actual request.
- Simple Methods: Remember that for “simple” methods (
POST), a preflight request is not necessary. The
Access-Control-Request-Methodis only used for “non-simple” HTTP methods.
Access-Control-Request-Method header is a critical part of the CORS mechanism, allowing clients to inform the server about the method they intend to use in the actual request. Correctly implementing and understanding this header will enhance cross-origin interactions, ensuring smoother operation and stronger security in your web applications.