Private WP will make sure people can only read your blog after they log in. Already logged in users will see no difference. 
Users who are logged out will get the login page, and only that.
Use this for private “intranet style” blogs, or closed community sites.
Note that the plugin offers no options. Activate it to turn it on, deactivate it to turn it off!
If you also use Windows Live Writer, be sure to check out <a href="https://wordpress.org/extend/plugins/wlw-login/" rel="ugc">WLW Login</a>.

Private WP

This plugin is simple and robust (it works even it hasn't been updated for 2 years) ... yet it does exactly what it should do: lock the whole site with the login site.
For most of our beta sites this is exactly what we need while the clients editing the site until it is ready for golive. No unnecessary additional features that need your focus ... just active it and its runs.



Does what it should do

Makes your blog accessible only to logged in users.

Silver Muru

WS Force Login Page force users who are not logged in by redirect into login page, this way it is good tool for developers to install sites which are in development process by restrict access to site and its content. Or when you want to put all site articles under password this plugin will do this! Working also with domains what includes umlaut letters like ö, ä, õ, ü
Suitable also for putting site to maintenance mode and show custom message in login view.

WS Force Login Page

I had problem with other similar plugins what didnt work in sites with domains what included umlaut letters like ö, ä, õ, ü thats why I needed this kind of plugin



Useful

Redirecting user to login page if not logged in, working also with domains what includes umlaut letters like ö, ä, õ, ü

Private WP vs WS Force Login Page