<?php
function genRandomString($maxLength) {
    for($i=0; $i < $maxLength; $i++) {
        if($i == ($maxLength/2)) $str .= "___0x31337___";
        $str .= chr(rand(33,126));
    }
    return $str;
}

$url = "some URL";


$ch = curl_init();
print("<pre>");
while(1) {

    curl_setopt($ch, CURLOPT_URL,$url);

    curl_setopt($ch, CURLOPT_POST, 1);

    $u = genRandomString(rand(5,40));
    $p = genRandomString(rand(8,64));

    curl_setopt($ch, CURLOPT_POSTFIELDS,"user=".$u."&pass=".$p."");

    $result= curl_exec ($ch);


    print $result."\n";

}
print("</pre>");
curl_close ($ch);

?>