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/:
<?php final class CustomLoginHandler extends PhabricatorAuthLoginHandler { public function getAuthLoginHeaderContent() { return phutil_safe_html( '<h1>Your Custom HTML Here</h1>'); } }