function _post($url, $data, $optional_headers = null)
{
  $params = array('http' => array(
              'method' => 'POST',
              'content' => $data
            ));
  if ($optional_headers !== null) {
    $params['http']['header'] = $optional_headers;
  }
  $ctx = stream_context_create($params);
  $fp = @fopen($url, 'rb', false, $ctx);
  if (!$fp) {
    throw new Exception("Problem with $url, $php_errormsg");
  }
  $response = @stream_get_contents($fp);
  if ($response === false) {
    throw new Exception("Problem reading data from $url, $php_errormsg");
  }
  return $response;
}

This function dosen't use curl, or any other libraries.  Just include it in your function library and use it like this:
$Post_result = _post('http://www.yourdomain.com/your_path/post_api.php',"method=fetchJson&params=select * from user");

POST Function Using HTTP Headers Return Result In A Variable

php, post, function

PHP