forcedownload.php

<?php
error_reporting(E_ALL);
$file = $_GET['file']; // a remote file url

$headers = array_change_key_case(get_headers($file, TRUE));

$filesize = $headers['content-length'];

if ( $headers[0] != 'HTTP/1.1 404 Not Found' ) {
    header('Content-Description: File Transfer');
    header('Content-Type: application/octet-stream');
    header('Content-Disposition: attachment; filename='.basename($file));
    header('Content-Length: ' . $filesize);
    ob_end_clean();
    flush();
    readfile($file);
    exit;
}

while(1) {
    Echo "\n";
    if ( connection_status() != 0 ) {
        die;
    }
}
?>