$user = "TestUsername";
    $pass = "TestPassword";

    $curl = curl_init();
    $curl_config = array(
        CURLOPT_URL             => "http://website_name.com/form_action_url",
        CURLOPT_POST            => true,
        CURLOPT_RETURNTRANSFER  => true,
        CURLOPT_POSTFIELDS      => array('user' => urlencode($user),
                                        'pass' => urlencode($pass)
                                        ),
        CURLOPT_HEADER          => true,
    );
    curl_setopt_array($curl, $curl_config);
    $response= curl_exec($curl);