How to use drupal_http_request for send data?
Your $url_login looks like the default URL scheme for a Ruby on Rails website that uses the devise login system. Here is a function I've used to login to a rails/devise backed web site.

/** Authenticate via Rails/Devise site */
function devise_login($email, $pass) {
   //Build up data to send to devise
   $data = array('user' =&gt; array('email' =&gt; $email, 'password'=&gt;$pass));
   //Pull the url out of the drupal settings
   $url = variable_get('devise_authentication_url', '');
   if ($url != '') {
     $response = drupal_http_request($url, array(
       'method' =&gt; 'POST', 
       'data' =&gt; json_encode($data), 
       'max_redirects' =&gt; 0,
       'headers' =&gt; array('Content-Type' =&gt; 'application/json', 'Accept' =&gt; 'application/json'))
     );

     return = json_decode($response-&gt;data); 
   }

   return FALSE;
}