Hi there,

Welcome to Box Community and glad to assist!

As of this message, there's no Admin settings that will force users to password-protect their public shared links. For the meantime, please submit this as a feature request.

For any product feature request or suggestions, we recommend you post your idea on pulse.box.com for more visibility. Our product team reviews all submissions and will consider whether to include feedback in their product roadmap. 

Thanks for posting!