使用AJAX的CSRF无法在codeigniter中工作

Question

我使用了codeigniter 3.0并且我已经实现了csrf功能，问题是csrf无法使用ajax调用。

var page_name = $('#page_name').val();
if(!$.trim(page_name).length)   
{
    $('#page_name_err').html('Please enter page name.');
    $('#page_name').addClass('form-control-error');
    $('#page_name').removeClass('form-control-success');
}
else
{
        var post_data = {
                            'pagename': encodeURIComponent(page_name),
                            <?php  if($this->uri->segment(3) == "edit"){ ?> 'id':encodeURIComponent(id), <?php }?>
                            '<?php echo $this->security->get_csrf_token_name(); ?>' : '<?php echo $this->security->get_csrf_hash(); ?>'
                        };


        //empty($user['user_id'])
        <?php if($this->uri->segment(3) == "edit"){?>
            var id= <?=$page['cms_id']?>;
        <?php } ?>
        <?php if(true){?>
        $.ajax({
            <?php if($this->uri->segment(3) != "edit"){?>
            url:'<?=base_url().$this->config->item('admin_folder')?>/cms/check_page_exists',
            <?php }else{?>
            url:'<?=base_url().$this->config->item('admin_folder')?>/cms/check_editpage_exists',
            <?php }?>
            type: "POST",
            data: post_data,
            success: function(html){
                if(html==1){
                    $('#page_name_err').html('Page name already exists. ');
                    $('#page_error').html('Page name already exists. ');
                    $('#page_name').addClass('form-control-error');
                    $('#page_name').removeClass('form-control-success');
                    $('#page_name').focus();
                }
                else{
                    $('#page_name_err').html('');
                    $('#page_error').html('');
                    $('#page_name').addClass('form-control-success');
                    $('#page_name').removeClass('form-control-error');
                }
            }
         });
        <?php }else{ ?>
            //$('#email_err').html('');
            //$('#email').addClass('form-control-success');
            //$('#email').removeClass('form-control-error');
        <?php }?>
}

}

错误是：不允许您请求的操作。 所以请帮我解决这个问题 谢谢。