Filters and $_POST (or $request post vars)

Try using $_REQUEST['Maint_Userid']... or whatever the form/post variable's name it is you want to access from inside the Filter.

Code:

public function before(RequestInterface $request, $arguments = null)
    {
        $maint_Userid = $_REQUEST['Maint_Userid'];
        $create_Userid = $_REQUEST['Create_Userid'];
        ...