WordPress prompts for FTP login for plugin/theme upload on one server; Not on an

I have two pretty identical FreeBSD servers both running Apache. But strangely on Server #1, if anyone tries to install a plugin or theme from Dashboard, it prompts for FTP login info. If anyone does the same from a WP install on Server #2, it doesn’t prompt for FTP.

The problem is I actually *want* it to upload through FTP because if the webserver directly writes to the directory, it owns it www:www. And then my users can’t edit the files from shell.

I see a ton of posts on how to suppress it so no FTP login prompt comes up.. But I want to force it to appear.

When stuff is uploaded via FTP, the files get ownership of <username>:www, which makes life good.

I’ve matched up the ownerships and permissions on the themes/plugins/uploads directories on Server #2 to match #1, but that didn’t change anything. Is there some simple setting to turn FTP prompt on/off?

The problem is anything I’ve googled on the subject is oriented towards *disabling* FTP login prompts. And I want to *enable* them.