how to build a site while making it private

now I know there's tons of way of doing this to allow a test site (like sub domain) would solve this, but in this case, It's too late to create a dev environment, so I was wondering if anyone knew of a plugin that allows you to lock you wordpress from the public (like password protect the home page and entire site and those who have the password would be able to gain access as a regular visitor (without having to register) others would just see the coming soon page (under construction). I'm open to other solutions as well.