Yes you can, head to settings > privacy and add your chosen password, click + icon to add the password.

Once the password is added, when you next visit your site you will be greeted with a password entry form. You can enter password to access your site, and share that password with others, the password is only required every 1 hour on the viewers device to save irritation when visiting different pages on the site.

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If your reason for wanting to password protect your site is because you are currently building your site and worried about people seeing it. As long as your site is still on the .onfabrik.com domain initially provided and you have not giving that address out then no one will be able to find your website to see so you do not really need to worry about a password but thats up to you.

If for other reasons please let us know.