Backbone e Slim PHP - Access-Control-Permitir-Cabeçalhos - Pode obter informações, não pode POST-lo?

Estou usando o Backbone e o framework PHP Slim. Estou tentando postar informações para minha API, no entanto, o Access-Control-Allow-Headers continua me causando problemas ...

Meu console lê:

    OPTIONS http://api.barholla.com/user/auth 405 (Method Not Allowed) zepto.min.js:2
XMLHttpRequest cannot load http://api.barholla.com/user/auth. Request header field Content-Type is not allowed by Access-Control-Allow-Headers.

Meus cabeçalhos dizem:

Request URL:http://api.barholla.com/user/auth
Request Method:OPTIONS
Status Code:405 Method Not Allowed
Request Headersview source
Accept:*/*
Accept-Charset:ISO-8859-1,utf-8;q=0.7,*;q=0.3
Accept-Encoding:gzip,deflate,sdch
Accept-Language:en-US,en;q=0.8
Access-Control-Request-Headers:origin, content-type, accept
Access-Control-Request-Method:POST
Connection:keep-alive
Host:api.barholla.com
Origin:http://localhost
Referer:http://localhost/barholla/app/
User-Agent:Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.4 (KHTML, like Gecko) Chrome/22.0.1229.94 Safari/537.4
Response Headersview source
Access-Control-Allow-Origin:*
Allow:POST
Connection:close
Content-Type:application/json
Date:Thu, 08 Nov 2012 16:12:32 GMT
Server:Apache
Transfer-Encoding:chunked
X-Powered-By:Slim
X-Powered-By:PleskLin

Meus cabeçalhos no meu arquivo slim index.php são:

$res = $app->response();
$res->header('Access-Control-Allow-Origin', '*');
$res->header("Access-Control-Allow-Methods: PUT, GET, POST, DELETE, OPTIONS");

Para lidar com os dados do post:

$app->post('/user/auth', function () use ($app) {
//code here
});

No meu javascript (eu estou usando o framework backbone) meu código é:

 App.userAuth = new App.UserAuthModel({
  username: $('#username').val(),
  password: hex_md5($('#password').val())
});

App.userAuth.save({}, {
  success: function(model, resp) {
    console.log(resp);
  },
  error: function(model, response) {
    console.log(response);
  }
});

Qualquer ajuda seria muito apreciada, estive preso nisso por muito tempo!

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