nginx sample config for phpBB installation in subfolder

The shipped nginx.sample.conf of phpBB is great but won' work out of the box for the quite common use-case to run phpBB in a sub-folder like e.g. /forum/ side by side with other software like e.g. a blog at /blog/.

It would be great if phpBB could ship such a sample config for a subfolder as well. Maybe the following one could be used as an inspiration:

https://www.phpbb.com/community/viewtopic.php?p=15235601#p15235601