Setting up a homepage that password protects the whole site

I’ve checked the forum history for the answer to this – but got too much unrelated info. So! If anyone has a moment…

I simply need a landing page that requires the user to have a password to enter the site. I’ve already created the site, but have been asked to make it only accessible by individuals with a password. Hence, all pages are not to be seen until an initial password gets people in.

What would be the best plugin or solution? Thanks! Marty