Transparent Authentication

Question: We have set up Web Safety appliance / Squid proxy to transparently intercept HTTP and HTTPS traffic. We would like to enforce proxy authentication. Is it possible?

Answer: Unfortunately, this is not possible.

Proxy authentication works by challenging the browser with authentication prompts. When browser tries to connect to a resource that needs to be authenticated Squid denies the connection asking browser to authenticate. In case of transparent deployments browser does not know that there is Squid in between and will then silently refuse to provide user credentials when challenged. This behavior is by design.