Joomla User Authentication Script For External websites

$query="SELECT password FROM `jos_users` WHERE username='".$_POST["userid"]."'";
$result = mysql_query($query);

if (mysql_num_rows($result)>0){
$dbpassword=mysql_result($result, 0);
mysql_close($link);
list($md5pass, $saltpass) = split(":", $dbpassword);
if ((md5($_POST["passwd"].$saltpass))==$md5pass) {
echo "Success" ;
} else {$messaggio="Password error:";}
}