LDAP 登录时出现问题

登录时，此脚本的问题在于，用户可以在用户名字段中仅使用用户名登录，而在密码字段中不使用密码登录。他们还可以使用正确的用户名和密码登录。但是，当使用正确的用户名和错误的密码时，登录将失败。我搜索了一下，但找不到太多。这是我所拥有的。

<?php 
    session_start();
    include('config/db.php');
    //echo phpinfo();
    if(isset($_REQUEST['hdn_submit']) && $_REQUEST['hdn_submit']=="1"){ 
        $ldaprdn = $_POST['username'] . '@domain';
        $uname = $_POST['username'];
        $ldappass = $_POST['password'];
        //$ldapconn = ldap_connect(" old IP address",port)or die("Could not connect to LDAP server.");
        $ldapconn = ldap_connect("IP address",port)or die("Could not connect to LDAP server.");
        //echo $ldaprdn;
        if ($ldapconn)
        {
            //ldap_set_option($ldapconn,LDAP_OPT_PROTOCOL_VERSION,3) or die("Could not set ldap protocol version");
            // binding to ldap server
            $ldapbind = @ldap_bind($ldapconn,$ldaprdn,$ldappass);
            // verify binding
            if ($ldapbind)
            {
                //login successfull 
                $_SESSION['checkin'] = date('d/m/Y h:i:s A');
                $_SESSION['user_name'] = $_REQUEST['username'];
                header('Location: index.php');
            }
            else
            {
                //echo 'hello';
                echo '<script language="javascript">alert("Invalid Login. Please try again!")</script>;';
                $_SESSION['LoggedIn'] = '0';
            }
        }
    }
 ?>
<?php  include_once('template/header.php'); ?>
<div class="row page-area">
  <div class="panel panel-primary" style="width:300px; margin:100px auto;">
    <div class="panel-heading">User Login</div>
    <div class="panel-body">
      <form class="form-signin" method="post" action="">
          <?php if($msg!=''){ ?>
          <p class="bg-primary"><?php echo $msg; ?></p>
          <?php } ?>
          <input name="username" type="text" class="form-control" placeholder="User Name" required autofocus><br/>
          <input type="password" name="password" class="form-control" placeholder="User Password" required><br/>
          <button class="btn btn-lg btn-primary btn-block" type="submit">
              Sign In
          </button>
          <input type="hidden" name="hdn_submit" value="1">
      </form>
    </div>
  </div>
</div>
<?php  include_once('template/footer.php'); ?>