authentication varnish before squid

[angelo iannello]

Hi all,
i have configured varnish that caching for speed improvement all request 
passed to a backend based on squid proxy.

lan => varnish => squid => internet

Squid have a basic authentication but the popup relative does not appear to 
the client browser, squid says cache denied authentication.

If i use squid directly i have succesfull access on the popup and i can 
authenticate on it.

It's possible that varnish not recognize this authentication?

do exist a workaround for solving this problem?

tnx

Angelo