Re: Talking HTTPS to proxies

FWIW, Google Chrome supports HTTPS proxies (

On Thu, Apr 14, 2011 at 9:04 PM, Willy Tarreau <> wrote:

> Hello,
> I'm regularly encountering what I would call dirty and unreliable
> hacks to provide proxy authentication in enterprises. And with the
> rise of external proxy services, it's going to get even worse.
> A common issue is that in many enterprises, a password must never pass
> in clear text over the network. So byebye Basic Auth. Digest requires
> that a database of cleartext passwords exists, which is most commonly
> refused too. Some proxies support NTLM auth in MS environments, but it
> is not the case for all of them, and some proxies simply cannot access
> such a service from where they're placed.
> Due to this, we're commonly seeing cookie-based authentication methods
> which rely on redirects and which are not much reliable if we put the
> efficiency aside.
> The overall principle is approximately the following (I'm saying approx
> because I've seen several variants depending on the will to use popups
> or forms, and the trade between security and comfort) :
>  1) the browser tries to access through the proxy
>  2) the proxy wants user to authenticate and redirects it to a host under
>     the proxy's responsibility over https.
>  3) the browser follows the redirect through the proxy and gets either an
>     auth form or a 401
>  4) the user enters his credentials and validates. The request still
> contains
>     a query string with all the info about the original URL at
>  5) the proxy accepts them, and issues a redirect to a fake host under
>, with the request still encoded in the query string along
>     with a token. It also emits a cookie for the authentication host.
>  6) the browser follows the redirect and requests the fake host over HTTP
>  7) the proxy intercepts the request, returns a redirect to the initial URL
>     with a set-cookie header so that as long as the user remains on the
> same
>     site it will present this cookie.
>  8) the browser follows that redirect and finally goes to with
>     the cookie.
>  9) when the user goes to another site, steps 1 and 2 apply, the proxy
>     sees the cookie that was delivered at previous step 5 and is able to
>     directly jump there.
> Overall, those are a lot of redirects, in order to safely authenticate a
> user over the network. Due to this, I've seen some setups where the
> credentials are assigned to the client's IP only. That way once the user is
> authenticated, everybody can access the proxy under his credentials just
> by being relayed by his PC. This is a common trick in big enterprises.
> Another workaround consists in authenticating the connection regardless
> of any request in it. Some clients can then share the same connection by
> inserting a proxy in the middle and all browse over the same connection
> (I already encountered this case too).
> And the cherry at the top of the cake is that this doesn't work well.
> Some sites make use of flash which does not send the cookies (so the
> proxy vendors use other tricks for that), and when the users's cookie
> for the authentication host expires, you see lots of funny things. If
> it expires when loading an image, you often never get it and don't see
> the auth form either. Also, XHR and POSTs don't work well either : POSTs
> to a site not covered by the current cookie will have its contents lost,
> and both XHR and POSTs will be lost when the auth cookie expires (very
> annoying in webmails where you know that all your mail's contents are
> lost when you see the popup after clicking "send").
> What I've realized is that all those horrors only exist because browsers
> offer no provisions for connecting to proxies over HTTPS instead of HTTP.
> It would be amazingly simple. We'd just have to check the box "use HTTPS"
> in the browser's config, retrieve the proxy's certificate and everything
> could safely be exchanged with the proxy. Even basic auth would be easy
> to use and safe. We could also make use of client certificates with this.
> So what I'm wondering now is why we have not seen this yet. Is it because
> nobody has brought the issue yet, because the vendors who implement the
> horrors I described above are too happy to be ahead of competition when
> it comes to deploying safe authentication methods, because there are
> major drawbacks in doing this, or because I'm stupid and have never
> found how to enable this ?
> I'm sure that some proxies do probably already support it as a side effect
> of being used as SSL reverse-proxies. We only need browsers to add the
> checkbox in their proxy config to enable this. I have heard about some
> sites where an stunnel-like component is installed on the user's PC (either
> as a java applet or as a real daemon) and simply transforms the cleartext
> HTTP traffic into HTTPS to connect to the proxy. (I did not see those
> myself,
> I only saw applets to use stronger crypto than what the browser offers, but
> they were not deployed as explicit proxies).
> Shouldn't we try to encourage both browser vendors and proxy vendors to
> enable
> Thanks for any insight,
> Willy

Received on Thursday, 14 April 2011 19:38:14 UTC