Re: [squid-users] transproxy + auth on parent proxy

From: Colin Campbell <>
Date: Thu, 7 Feb 2002 09:13:35 +1000 (EST)


On Wed, 6 Feb 2002, rodolphe wrote:

> hi all,
> i was wondering if someone had this idea in mind.
> case :
> -transproxy is a necessity.
> -need authentification too.
> would it be possible to set up two squids, one managing transproxy and
> cache and the parent (light with little or no cache) managing
> authentification ?
> -even better : squids runnning on the same machine.
> Where the auth process would break as it's not the client that directly
> asks for authentification ?

If you understand the authentication process, you'll know why it isn'y
possible to authenticate at all when using a transparent proxy.

HTTP specifies two "authentication required" error codes. One for a HTTP
server (401), the other for a HTTP proxy (407). When a browser connects to
a server requiring authentication, the server examines the HTTP header
supplied in the request. If it includes the correct authentication
information (username and password) the request is honoured and the server
sends back a return code of 200. If the authentication information is not
present in the header, the server responds with a return code of 401. When
the browser sees this it pops up the authentication window where you type
your username and password. The browser then re-submits the original
request this time containing the authentication information it just
collected. All future requests to the server will contain the
authentication information.

Proxy authentication is handled in a similar manner. A browser that knows
it's using a proxy (in tranparent proxying, this is NOT the case) makes a
connection to the proxy and issues an HTTP request. That request can
contain proxy authentication information. Note that this is in a different
part of the HTTP request to the web server authentication information. If
the proxy requires authentication and the proxy-auth HTTP header is empty,
the proxy responds with a return code of 407. When the brwoser receives
this it pops up a window asking for the proxy username and password. Once
you've typed it in, the browser resubmits the original request this time
containing the proxy authentication information. All further requests to
the proxy will contain the authentication information.

If a browser is not configured to use a proxy, it will quite rightly
ignore any return code of 407. Why should it give away your proxy username
and password to anyone who asks for it?

In your case you have browser->transparent proxy->auth proxy. The auth
proxy can certainly request authentication of the transparent proxy. The
cache_peer config line supports this with the "login=user:password"
option. However, all that does is authenticate the proxy with its parent.
There is no way to make the transparent proxy authenticate individual
users. Even if the 407 sent by the auth proxy, could be passed from
transparent proxy to browser (it can't because the transparent proxy traps
it) you cannot make the browser respond because as far as it knows, it
isn't using a proxy.

As has been stated many, many times on this list:

        transparency, authentication, pick one

Received on Wed Feb 06 2002 - 16:17:49 MST

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