LiteXiv/proxy.php

<?php
require_once __DIR__ . '/include/config.php';

if (
	!isset($_GET['dest'])
	|| !(
		strpos($_GET['dest'], 'i.pximg.net/') === 0
		|| strpos($_GET['dest'], 's.pximg.net/') === 0
	)
) {
	http_response_code(400);
	die('Illegal request');
}

$stream_context = [
	'http' => [
		'header' =>
			"User-Agent: Mozilla/5.0" . PHP_EOL .
			'Referer: https://www.pixiv.net/'
	]
];
if (HTTP_PROXY) {
	$stream_context['http']['proxy'] = 'tcp://' . HTTP_PROXY;
}
$response = file_get_contents('https://' . $_GET['dest'], false, stream_context_create($stream_context));

if (!$response) {
	http_response_code(500);
	die('Proxy failed');
}

foreach ($http_response_header as $header) {
	if (strpos($header, 'Content-Type: ') === 0) {
		header($header);
		break;
	}
}

$path = explode('/', $_GET['dest']);
header('Content-Disposition: filename="' . $path[count($path) - 1] . '"');
echo $response;