joch

If you need to make your WordPress site private, this plugin makes it possible for 
your users having to log in before being able to view any content on the website.

WP Require Auth

This plugin makes it mandatory to be logged in before viewing any content.

Henrik Schack

This is a plugin for WordPress that provides multifactor authentication with one-time passwords using the <a href="http://www.yubico.com/" rel="nofollow ugc">Yubikey USB token</a>. 
The plugin uses the Yubico Web service API in the authentication process. 
The one-time password requirement can be enabled on a per user basis.

yubikey-plugin

Thanks for an amazing plugin. Hopefully the maintainer is looking and will update things to show they are tested as working with WP 5.4, since it does.

Love that I can use my YubiKey on WP

Enhanced Login Security for Your Wordpress blog.

WP Require Auth vs yubikey-plugin