Do you want to share your calendar only with a select group of people? This feature allows you to restrict access to your published calendar to a select list of members that you maintain. 

When a visitor attempts to access your calendar via its URL (your calendar's URL is: http://www.localendar.com/public/membername), they will be required to sign in before being allowed to proceed.

Remember  that Private events you enter on your calendar are never visible to anyone except yourself, regardless of your calendar security settings. Only events designated as Public are shown on the public version of your calendar.