Varnish is a great performance boost for web sites. Sometimes however you may need to configure authentication so that your cached pages are not visible to the public. Basic authentication needs to be mirrored from the webserver to the Varnish VCL.

To do this you need to use a Varnish module and to use that you need to compile them against the Varnish source - not for the faint hearted - here are some remedies to problems you may face.