Register custom query vars

add-query-vars.php

<?php
/**
 * Register custom query vars
 *
 * @param array $vars The array of available query variables
 * 
 * @link https://codex.wordpress.org/Plugin_API/Filter_Reference/query_vars
 */
function myplugin_register_query_vars( $vars ) {
	$vars[] = 'key1';
	$vars[] = 'key2';
	return $vars;
}
add_filter( 'query_vars', 'myplugin_register_query_vars' );