This config option is being replaced with a modular handler which can render an equivalent message, but also present more flexible context-dependent messages.
If you currently use this option, you can get equivalent behavior by putting a file like this in `phabricator/src/extensions/`:
```name=CustomLoginHandler.php
<?php
final class CustomLoginHandler
extends PhabricatorAuthLoginHandler {
public function getAuthLoginHeaderContent() {
return phutil_safe_html(
'<h1>Your Custom HTML Here</h1>');
}
}
```