Topic for the Password Protect extension
Adds an option to the PivotX editor to protect pages and entries with passwords. You can give different passwords for entries/pages or define a default password for all protected content. You can also select to allow access (without giving the password) to users that are already logged into PivotX.
Latest version also supports protecting weblogs (categories and chapters were already added earlier).
Get the extension here: http://extensions.pivotx.net/?e=4