How to set the Access-Control-Allow-Origin header with XMLHttpRequest

Question

This is the code to validate geoJSON according to the sample provided:

 function processSuccess(data){
            if(data.status==="ok")  console.log("You just posted some valid geoJSON");
            else if(data.status==="error") console.log("There was a problem with your geoJSON "+data.message);
        }
        function processError(data){
            console.log("The AJAX request could not be successfully made");
        }
        $.ajax({
            url: 'http://geojsonlint.com/validate',
            type: 'POST',
            data: geo,
            dataType: 'json',
            success: processSuccess,
            error: processError
        });   

I am trying to validate geoJSON using the following code:

  var getXHR=function()
{
    try{return new XMLHttpRequest();}   catch(e){}
    try{return new ActiveXObject("Msxml2.XMLHTTP.6.0");}    catch(e){}
    try{return new ActiveXObject("Msxml2.XMLHTTP.3.0");}    catch(e){}
    try{return new ActiveXObject("Microsoft.XMLHttp");}     catch(e){}
    console.err("Could not find XMLHttpRequest");
};
var makeRequest=function(uri,data)
{
    //make the actual XMLHttpRequest
    var xhr=getXHR();
    if('withCredentials' in xhr)    console.log("Using XMLHttpRequest2 to make AJAX requests");
    xhr.open("POST",uri,true);
    xhr.onreadystatechange=function(){
        if(xhr.readyState===4)
        {
            if(xhr.status===200 || xhr.status===304)
            {
                var response=JSON.parse(xhr.responseText);
                if(response.status==="ok")  console.log("You just posted some valid geoJSON");
                else if(response.status==="error")  console.log("There was a problem with your geoJSON "+response.message); 
                else    console.log("Response has been recieved using "+response.status);
            }
        }
        else    console.log("Response recieved with status "+xhr.status);
    };
    xhr.setRequestHeader("Content-Type","application/json");
    xhr.setRequestHeader("X-Requested-With","XMLHttpRequest");
    //supported in new browsers...do JSONP based stuff in older browsers...figure out how
    xhr.setRequestHeader("Access-Control-Allow-Origin","http://geojsonlint.com/");
    xhr.setRequestHeader("Accept","application/json");
    xhr.send(JSON.stringify(data));
};

Here,I make the actual request:

 makeRequest('http://geojsonlint.com/validate',geo);

ERROR:

I get this error in the Chrome console:

 Using XMLHttpRequest2 to make AJAX requests gmaps_geoJSON.js:14
 Failed to recieve response gmaps_controls.js:25
 XMLHttpRequest cannot load http://geojsonlint.com/validate. Request header field   
 Access-Control-Allow-Origin is not allowed by Access-Control-Allow-Headers.   

HEADERS

This is the data related to the request:

Request URL:http://geojsonlint.com/validate
Request Method:OPTIONS
Status Code:200 OK

Request Headers
Accept:*/*
Accept-Encoding:gzip,deflate,sdch
Accept-Language:en-US,en;q=0.8,en-AU;q=0.6,en-GB;q=0.4,te;q=0.2
Access-Control-Request-Headers:access-control-allow-origin, accept, x-requested-with,  content-type
Access-Control-Request-Method:POST
Connection:keep-alive
DNT:1
Host:geojsonlint.com
Origin:http://localhost:8180
Referer:http://localhost:8180/GoogleMapsLoadingTest/MainService? scenario=c&operation=1&objkey=000011&objtype=EQUI&gisuniqkey=hgsfsfsfs2436353535
User-Agent:Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko)  Chrome/34.0.1847.116 Safari/537.36

Response Headers
Access-Control-Allow-Headers:Origin,Content-Type,Accept
Access-Control-Allow-Methods:POST,GET,OPTIONS,PUT,DELETE
Access-Control-Allow-Origin:*
Connection:keep-alive
Content-Encoding:gzip
Content-Type:text/html; charset=utf-8
Date:Thu, 24 Apr 2014 14:48:57 GMT
Server:nginx
Transfer-Encoding:chunked

Answer 1

You shouldn't be setting Access-Control-Allow-Origin as a request header, that's a response header.

You can see from the response what request headers the server will accept:

Access-Control-Allow-Headers:Origin,Content-Type,Accept

And the error message tells you that:

Request header field Access-Control-Allow-Origin is not allowed

It looks like it might not accept X-Requested-With either.