Magento 2 maintenance IPs when site is behind proxy

di.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">

  <!-- ... -->
  <!-- Inside di.xml, place the following -->
    <!-- Restore original visitor IP from CloudFlare header -->
    <type name="Magento\Framework\HTTP\PhpEnvironment\RemoteAddress">
        <arguments>
            <argument name="alternativeHeaders" xsi:type="array">
                <item name="http_cf_connecting_ip" xsi:type="string">HTTP_CF_CONNECTING_IP</item>
            </argument>
        </arguments>
    </type>
  <!-- ... -->