passing url variables

<?php
$rusr="";
$rpwd="";

$modx->clearCache();

$rusr=$_GET['usr'];
$rpwd=$_GET['pwd'];

echo "username:  ".$rusr;

function login($username, $password)
{
   global $modx, $table_prefix;
   $username = $modx->db->escape($username);
   $password = $modx->db->escape($password);
   $table_prefix="kdb";
 
   $res = $modx->db->select("id", $table_prefix."_web_users", 
      "username='$username' AND password='".md5($password)."'");
   if($modx->db->getRecordCount($res))
   {
      return "sucess";
      //other log in things...
   }
   else
   {
       return "fail";
   }
}


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