Why Are My Custom Headers Appearing as 'Access-Control-Request-Headers' in jQuery AJAX Requests?

Access Control Request Headers: Understanding the Addition to AJAX Headers with jQuery

In jQuery AJAX requests, custom headers can be added to enhance request customization. However, some headers may not appear in the expected format. This article aims to explain why custom headers may instead appear as "Access-Control-Request-Headers".

When a cross-origin request is made, the browser performs a preflight request using the OPTIONS method. This preflight request determines if the actual request is allowed. During this preflight request, the browser sends headers indicating which HTTP methods and headers the actual request will use.

One such header is the "Access-Control-Request-Headers" header. It lists the custom headers that the actual request will include. This is because the browser needs to obtain permission from the server to send these custom headers.

Therefore, when you send a custom header in an AJAX POST request, it is added to the "Access-Control-Request-Headers" header in the preflight OPTIONS request. This is a browser behavior intended to prevent cross-origin security vulnerabilities.

Resolving Custom Header Issue

To include custom headers directly in the actual request, it is essential to configure the server to handle preflight requests and grant permission for the specified custom headers. This configuration is server-specific and requires permissions to be set appropriately.

Example with jQuery

The provided jQuery example demonstrates how to set a custom header:

$.ajax({
  type: "POST",
  beforeSend: function(request) {
    request.setRequestHeader("Authority", authorizationToken);
  },
  url: "entities",
  data: "json=" + escape(JSON.stringify(createRequestObject)),
  processData: false,
  success: function(msg) {
    $("#results").append("The result =" + StringifyPretty(msg));
  }
});

By following these guidelines, developers can effectively add custom headers to AJAX requests, ensuring that the browser adheres to cross-origin security protocols.

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