Re: Talking HTTPS to proxies


I think it's a good idea, but there could be some gotchas, especially 
with proxies that intercept SSL connections on port 443 and do MITM so 
they can scan https traffic.

In fact scanning https traffic is a big problem for companies, since 
more malware uses https to download more malware to avoid scanning.

I'm wondering if it wouldn't be a good time to start getting browsers to 
off-load the actual TLS function to the proxy.

e.g. if a browser is using a proxy, and wants to go to, currently they do


then (maybe) negotiate their own SSL/TLS connection, then send (maybe) 
an HTTP request.  I say maybe, because in many cases, the client can do 
whatever they like with the connection.

If instead the client sent


then several benefits come about:

a) the proxy knows (and can enforce) that the client is using http over 
SSL/TLS.  In fact the proxy implements it.
b) the proxy doesn't need to use dest port in policy for CONNECT, since 
CONNECT can be blocked off completely, and https://site:port syntax can 
be used instead.
c) the proxy can do cert validation for the client
d) the proxy can scan the data, cache it etc.

It would be trivially simple for a proxy to support https:// syntax, as 
well as a client to use it.  It would need to become an optional setting 
in the client though, whether to use a tunnel, or https:// request 

tunneling is a security quagmire, it would be great to be able to lock 
it down.  At the moment, there aren't many options, since the proxy only 
sees server:port.  CONNECT is abused by many applications.


On 15/04/2011 7:04 a.m., 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

Adrien de Croy - WinGate Proxy Server -

Received on Thursday, 14 April 2011 23:47:38 UTC