viewforum.php's forum_data SELECT statement is currently a raw SQL string with no event that can be used by extensions to modify the forum lookup.

Source: https://github.com/phpbb/phpbb/blob/df5c769b554964983599884be60e434d991ad096/phpBB/viewforum.php#L50-L72

I'm building an extension that requires the ability to filter access to forums based on the domain, and so having this SQL be customizable via an extension would be helpful. I already have a working patch and will send a PR for discussion on the change.