This simple add-on just allows add/set custom headers to all HTTP requests from XenForo via src/config.php. For example, you may want set Accept-Language for using another language, if remote web-resource respects this header.
Example usage (src/config.php):
PHP:
<?php
// database options ...
// additional options for caching (for example), proxying all HTTP requests and another...
$config['http']['headers'] = [
// Prefers russian language; if not present - then...
