<form id="formLogin" action="login_dashboard.php" method="post" novalidate>
  <div class="form-group has-feedback">
    <input id="user_name" type="text" class="form-control" placeholder="Username"  name="user_name" required>
  </div>

  <div class="form-group has-feedback">
    <input type="password" class="form-control" placeholder="Password" name="user_password" required>
  </div>

  <div class="row">
    <div class="col-xs-6">
        <button type="submit" class="btn btn-primary btn-block btn-flat">login</button>
    </div><!-- /.col -->
  </div>
</form>

<script>
   $('#formLogin').on("submit",function(e) {
    if ($('#formLogin').smkValidate()) {

        $.post("login_dashboard.php", $("#formLogin").serialize() )
            .done(function( data ) {

                if (data.status === "danger") {
                    $.smkAlert({text: data.message , type: data.status});
                    $('#formLogin').smkClear();
                    $("#user_name").focus();

                } else {
                    $(location).attr('href', 'index.php');
                }

            });
        e.preventDefault();
    }
    e.preventDefault();
    });
</script>

<?php
include '../db/database.php';

$user_name = mysqli_real_escape_string($link, $_POST['user_name']);
$user_password = mysqli_real_escape_string($link, $_POST['user_password']);

$code = 'abcabcabcabcabcabc';
$hash_login_password = hash_hmac('sha256', $user_password, $code);

$sql = "SELECT * FROM user WHERE (user_name=? AND user_password=?)";
$stmt = mysqli_prepare($link, $sql);
mysqli_stmt_bind_param($stmt, "ss", $user_name, $hash_login_password);
mysqli_stmt_execute($stmt);
$result_user = mysqli_stmt_get_result($stmt);
if($result_user->num_rows == 1){
    session_start();
    $row_user = mysqli_fetch_array($result_user, MYSQLI_ASSOC);
    $_SESSION['user_id'] = $row_user['user_id'];
    $_SESSION['user_name'] = $row_user['user_name'];
    header('Content-Type: application/json');
    echo json_encode(array('status' => 'success'));
} else {
    header('Content-Type: application/json');
    $errors = "Username or Password incorrect" . mysqli_error($link);
    echo json_encode(array('status' => 'danger','message' => $errors));
}

mysqli_stmt_free_result($stmt);
mysqli_stmt_close($stmt);
mysqli_close($link);