magento2/app/code/Magento/Newsletter/Controller/Manage.php

<?php
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
namespace Magento\Newsletter\Controller;

use Magento\Framework\App\RequestInterface;

/**
 * Customers newsletter subscription controller
 */
abstract class Manage extends \Magento\Framework\App\Action\Action
{
    /**
     * Customer session
     *
     * @var \Magento\Customer\Model\Session
     */
    protected $_customerSession;

    /**
     * @param \Magento\Framework\App\Action\Context $context
     * @param \Magento\Customer\Model\Session $customerSession
     */
    public function __construct(
        \Magento\Framework\App\Action\Context $context,
        \Magento\Customer\Model\Session $customerSession
    ) {
        parent::__construct($context);
        $this->_customerSession = $customerSession;
    }

    /**
     * Check customer authentication for some actions
     *
     * @param RequestInterface $request
     * @return \Magento\Framework\App\ResponseInterface
     */
    public function dispatch(RequestInterface $request)
    {
        if (!$this->_customerSession->authenticate()) {
            $this->_actionFlag->set('', 'no-dispatch', true);
        }
        return parent::dispatch($request);
    }
}