$username = $form_state['input']['name'];
$password = $form_state['input']['pass'];

$authurl = variable_get('sgauth_base_url_authenticate', '');
$headers = array('Content-Type' => 'application/json');
$data = array('email' => $username, 'password' => $password);
$query = drupal_http_build_query($data);
$options = array('headers' => $headers, 'method' => 'POST', 'data' => $query);
$result = drupal_http_request($authurl, $options);

dpm($result);

POST /SingPostApi/MobileAuthenticate HTTP/1.0
Content-Type: application/json
User-Agent: Drupal (+http://drupal.org/)
Host: xxxxxxxxxxxx.xxxxxxxxxx.com
Content-Length: 36

email=xxx%40xx.xxx&password=xxxxxxxx

drupal_json_encode($input);

header('Content-Type: application/json');
echo drupal_json_decode($output);