This release fixes a few issues that were present when a forum install was in a vastly different directory, or on a different domain (or subdomain). A new variable has been introduced:
$wgPhpbbAuthAbsolutePath = '//www.domain.com/phpBB3/';
Which can be set to the absolute location of your phpBB installation. If this is not present, the extension will fall back to previously set variables, or will use the variables configured in your phpBB installation's "Server Settings".
Thank you to @phbaudin for assistance with this update.