<?php
$url = "http://e...content-available-to-author-only...e.com?param=test1\\test2\\test3\\test4";
$cleanUrl = preg_replace('|[^-\\\\a-z0-9~+_.?\[\]\^#=!&;,/:%@$\|*`\'<>"()\x80-\xff\{\}]|i', '', $url); echo $cleanUrl;
PD9waHAKCiR1cmwgPSAiaHR0cDovL2UuLi5jb250ZW50LWF2YWlsYWJsZS10by1hdXRob3Itb25seS4uLmUuY29tP3BhcmFtPXRlc3QxXFx0ZXN0MlxcdGVzdDNcXHRlc3Q0IjsKJGNsZWFuVXJsID0gcHJlZ19yZXBsYWNlKCd8W14tXFxcXGEtejAtOX4rXy4/XFtcXVxeIz0hJjssLzolQCRcfCpgXCc8PiIoKVx4ODAtXHhmZlx7XH1dfGknLCAnJywgJHVybCk7CmVjaG8gJGNsZWFuVXJsOw==