Creator’s website: https://wordpress.org/plugins/password-protected/
How to use: After enabling the Password Protected plugin, click Settings. Enter a New Password, repeat it in the following field, click the Enabled button, and scroll down to click Save.
If you choose, you can allow site administrators and/or logged-in users to bypass the password prompt. If you want everyone to be prompted even if they’re logged in, leave the Protected Permissions boxes unchecked. (In the example below, administrators are permitted, but everyone else will be asked for their password.)
Example: The Password Protected Demo website will ask you for a password (which, in this case, is OpenSesame!). This password protects the entire site’s contents from view.