<?php
$link = "http://d...content-available-to-author-only...e.com";
"#https?://\S+#i", '<a href="$0">(link)</a>',
$link
);
echo $link;
PD9waHAKCiRsaW5rID0gImh0dHA6Ly9kLi4uY29udGVudC1hdmFpbGFibGUtdG8tYXV0aG9yLW9ubHkuLi5lLmNvbSI7CiRsaW5rID0gcHJlZ19yZXBsYWNlKAogICAgIiNodHRwcz86Ly9cUysjaSIsICc8YSBocmVmPSIkMCI+KGxpbmspPC9hPicsIAogICAgJGxpbmsKKTsKZWNobyAkbGluazs=