src/etc/config.xml
<?xml version="1.0"?>
<!--
* Licensed under Academic Free License ("AFL") v. 3.0
* See LICENSE.txt or https://opensource.org/licenses/afl-3.0
*
* @category Siment_HttpHeaderThemeSwitch
* @copyright (c) 2017 Simen Thorsrud
* @author Simen Thorsrud <simen.thorsrud@gmail.com>
-->
<config
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Store:etc/config.xsd">
<default>
<siment_http_header_theme_switch>
<general>
<http_header>HTTP_X_UA_DEVICE</http_header>
</general>
</siment_http_header_theme_switch>
</default>
</config>