Keep getting No 'Access-Control-Allow-Origin' error with XMLHttpRequest

Question

I would have solved this issue by using jQuery $.ajax function but in this case jQuery is not option. Instead I am going with CORS request. I feel there is something wrong with the webserver that is responding to the request and I am having a hard time figuring out what the issue is.

Here is my code for creating the CORS request

var httpRequest = new XMLHttpRequest();
httpRequest.open('POST', url, true);
httpRequest.setRequestHeader( 'Access-Control-Allow-Origin', '*');
httpRequest.setRequestHeader( 'Content-Type', 'application/json' );
httpRequest.onerror = function(XMLHttpRequest, textStatus, errorThrown) {
  console.log( 'The data failed to load :(' );
  console.log(JSON.stringify(XMLHttpRequest));
};
httpRequest.onload = function() {
  console.log('SUCCESS!');
}

Here is the console.log error:

XMLHttpRequest cannot load http://test.testhost.com/testpage. Request header field Access-Control-Allow-Origin is not allowed by Access-Control-Allow-Headers.

Here are the header information:

> Remote Address:**.**.***.**:80 Request
> URL:http://test.testdomain.com/testpage Request
> Request Method:OPTIONS
> Status Code:200 OK

Request Headers:

OPTIONS /content-network HTTP/1.1
Host: test.testhost.com
Connection: keep-alive
Cache-Control: no-cache
Pragma: no-cache
Access-Control-Request-Method: POST
Origin: http://test.testdomain.com
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/36.0.1985.125 Safari/537.36
Access-Control-Request-Headers: access-control-allow-origin, content-type
Accept: */*
Referer: http://test.testdomain.com/
Accept-Encoding: gzip,deflate,sdch
Accept-Language: en-US,en;q=0.8

Response Headers:

HTTP/1.1 200 OK
Date: Thu, 14 Aug 2014 20:17:25 GMT
Server: Apache
Last-Modified: Thu, 14 Aug 2014 20:17:25 +0000
Cache-Control: no-cache, must-revalidate, post-check=0, pre-check=0
ETag: "1408047445"
Access-Control-Allow-Origin: *
Access-Control-Allow-Headers: Content-Type
Vary: Accept-Encoding
Content-Encoding: gzip
Access-Control-Allow-Headers: origin, x-requested-with, content-type
Access-Control-Allow-Methods: PUT, GET, POST, DELETE, OPTIONS
Content-Length: 6117
Connection: close
Content-Type: text/html; charset=utf-8

Answer 1

Your server's response allows the request to include three specific non-simple headers:

Access-Control-Allow-Headers:origin, x-requested-with, content-type

but your request has a header not allowed by the server's response:

Access-Control-Request-Headers:access-control-allow-origin, content-type

All non-simple headers sent in a CORS request must be explicitly allowed by the Access-Control-Allow-Headers response header. The unnecessary Access-Control-Allow-Origin header sent in your request is not allowed by the server's CORS response. This is exactly what the "...not allowed by Access-Control-Allow-Headers" error message was trying to tell you.

There is no reason for the request to have this header: it does nothing, because Access-Control-Allow-Origin is a response header, not a request header.

Solution: Remove the setRequestHeader call that adds a Access-Control-Allow-Origin header to your request.