ChallengeUser.js

function challengeUser (){
    var xhr = new XMLHttpRequest();
    var id = 58542; //Fuego bot user id
    var url = "http://online-go.com/api/v1/players/"+id+"/challenge/";
    xhr.open("POST", url, true );
    xhr.setRequestHeader("Content-Type", "application/json");
    xhr.setRequestHeader("Authorization", "Bearer " + accessToken);

    xhr.onreadystatechange = function () {
	if (xhr.readyState == 4) {
	    console.log('Status: '+xhr.status+
	    		'\nHeaders: '+JSON.stringify(xhr.getAllResponseHeaders())+
	    		'\nBody: '+xhr.responseText);
	}
    };

    var gameSettings = {
	"game": {
	    "name": "a test game",
	    "rules": "japanese",
	    "ranked": false,
	    "handicap": 0,
	    "time_control_parameters": {
		"time_control": "fischer",
		"initial_time": 259200,
		"max_time": 604800,
		"time_increment": 86400
	    },
	    "pause_on_weekends": true,
	    "width": 9,
	    "height": 9,
	    "disable_analysis": true
	},
	"challenger_color": "automatic",
	"min_ranking": 0,
	"max_ranking": 0
    };
    gameSettings = JSON.stringify(gameSettings);
    xhr.send(gameSettings);
}

Response

qml: Status: 0
Headers: "server: nginx/1.6.1\r\ndate: Sat, 22 Nov 2014 20:58:14 GMT\r\ncontent-type: text/html\r\ntransfer-encoding: chunked\r\nconnection: close\r\nvary: Accept-Language, Cookie\r\ncontent-language: en"
Body: