Código PHP:
<?php
include("config.php");
$user=stripslashes($_POST['username']);
$pass=stripslashes($_POST['password']);
$query = mysql_query("SELECT password FROM users WHERE username = '$user'") or die(mysql_error());
$data = mysql_fetch_row($query);
if($data[0] == md5($pass)) {
$_SESSION['user'] = $user;
$nonce = md5(uniqid(rand(), true));
setcookie('nonce', $nonce, time() + 7776000, '/');
$query = mysql_query("UPDATE users SET nonce = '$nonce' WHERE username = '$user'");
echo "login ok";
exit();
} else {
echo "fail";
exit();
}
?>