怎么实现用php来修改AD域用户名的密码

$host = "ldap://10.100.1.10:389"; $domain = "dec.com"; $user =$_POST["username"]; $oldpswd=$_POST["oldpswd"]; $pwdtxt=$_POST["newpswrd"]; $conn = ldap_connect($host) or die("Could not connect!" ); ldap_set_option ( $conn, LDAP_OPT_PROTOCOL

$host = "ldap://10.100.1.10:389";
$domain = "dec.com";
$user =$_POST["username"];

$oldpswd=$_POST["oldpswd"];
$pwdtxt=$_POST["newpswrd"];
$conn = ldap_connect($host) or die("Could not connect!" );

ldap_set_option ( $conn, LDAP_OPT_PROTOCOL_VERSION, 3 );
   ldap_set_option ( $conn, LDAP_OPT_REFERRALS, 0 ); 

   $bd = ldap_bind($conn,$user."@".$domain,$oldpswd);

 if($bd){
       if(ldap_mod_replace($bd,$pwdtxt))           {
             echo"succeded";
          } else {
             echo "failed";
         }

为什么老是失败呢？？？