get user credentials

<?php
header ("Content-Type:text/xml"); 

$rusr="";
$rpwd="";

$modx->clearCache();

$rusr=$_GET['username'];
$rpwd=$_GET['password'];


function login($username, $password)
{
   global $modx, $table_prefix;
   $username = $modx->db->escape($username);
   $password = $modx->db->escape($password);
   $table_prefix="modx";

   $xmFail="<response>
<responseCode>0</responseCode>
 <errorCode>103</errorCode>
<responseText>Access denied</responseText>
</response>";

$xmSucess="<response>
<responseCode>1</responseCode>
<responseText>OK</responseText>
</response>";

 
     $res = $modx->db->select("id", $table_prefix."_web_users", 
      "username='$username' AND password='".$password."'");

   if($modx->db->getRecordCount($res))
   {
      return $xmSucess;
   }
   else
   {
       return $xmFail;
   }
}


echo login($rusr,$rpwd);
?>