Jared Atchison

Retricts bbPress to logged in/registered members.
All users who try to view any bbPress page and are not logged in will be redirected to the site homepage or optionally a URL provided in the settings.
This plugin also disables all bbPress shortcodes for non-members except the login, register, and reset password shortcodes.
Note: This plugin does not work when bbPress is used in conjunction BuddyPress.

bbP Members Only

Retricts bbPress to logged in/registered members.

Hitesh Chandwani

bbPress Google reCAPTCHA v2 is a free plugin/add-on for bbPress, that allow you to easily add Google reCAPTCHA v2 on your bbPress forum.
bbPress Google reCAPTCHA v2 prevent spam from creating new topics or replies. This plugin is built to integrate seamlessly with your bbPress enabled WordPress website.
bbPress Google reCAPTCHA v2 is very easy to use and work for Anonymous posting as well as Logged-in users.

reCAPTCHA for bbPress

I was getting way too much spam on bbPress forms until I added this plugin. Thank you, good sir!

Does exactly what I need

Google reCAPTCHA v2 for bbPress is a free plugin/add-on for bbPress, that allow you to easily add Google reCAPTCHA v2 on your bbPress forum.

bbP Members Only vs reCAPTCHA for bbPress