RocketCake includes a built-in password protection mechanism, with which you can password protect all or specific pages of your website. You only need to put the "password protection" element on each website you want to protect.
See the How to password protect a website tutorial on how to do this.
Note: Only the websites themselves are protected by the password protection. If you include for example images and the user can obtain the URL of an included image on that page, he will be able to access that image directly.
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