If you do not wish to set up SSL on your active directory, and you are running on Windows, you can use COM and ADSI to set the new password for a user, or to active a user:
<?PHP
$ADSI = new COM("LDAP:");
    $user = $ADSI->OpenDSObject("LDAP://".$server."/".$newuser_dn, $adminuser, $adminpassword, 1);
    $user->SetPassword($newuser_password);
    $user->SetInfo();
$ADSI = new COM("LDAP:");
    $user = $ADSI->OpenDSObject("LDAP://".$server."/".$newuser_dn, $adminuser, $adminpassword, 1);
    $user->AccountDisabled = false;
    $user->SetInfo();
?>