Require Proxy Authentication?
This determines weather or not your users must authenticate themselves before they are allowed to use the proxy. There are three settings:

PAM Authentication uses the local username/password database to perform authentication. This is nice because users can change their proxy passwords via Userpass.

SMB Authentication attempts to authenticate against the SMB domain you enter in the text box. To configure this on the Windows-end you must create a file named 'proxyauth' and store it in the login share which contains the word "allow." If a user is authorized to log into this domain then they will be able to read this file and access wiill be grated. If they are unauthorized then the login will fail and proxy access will be denied.

Please note you cannot use this option with Transparent Proxying.