HTTP Request returns "Forbidden"

<?php

$databasehost = 'XXXXXXXXX';
$databasename = 'XXXXXXX';
$databaseusername = 'XXXXXXXXXXX';
$databasepassword = 'XXXXXXXXXXXX';

$con = mysql_connect($databasehost,$databaseusername,$databasepassword) or die(mysql_error());

mysql_select_db($databasename) or die(mysql_error());
$query = file_get_contents('php://input');

if (get_magic_quotes_gpc()) $query = stripslashes($query);
 
$sth = mysql_query($query);

if (mysql_errno()) { 
    header('HTTP/1.1 500 Internal Server Error');
    echo $query.'\n';
    echo mysql_error(); 
}
else
{
    $rows = array();
    while($r = mysql_fetch_assoc($sth)) {
        $rows[] = $r;
    }
    print json_encode($rows);
}
?>