Re: [squid-users] HTTPS forward proxy?

On 2014-01-22 09:25, David Deller wrote:
> Hello,
>
> I’m trying to set up Squid as an HTTPS forward proxy, but I’m having
> trouble getting it to work.
>
> Here's some background about my problem:
>
> * I have a web service running on Heroku, with a dynamic IP address.
> Static IPs on Heroku are not an option.
> * I need to connect to an external web service which is behind a
> firewall. The people who operate the external web service will only
> open their firewall to a specific static IP.
>
> My attempted solution is to use Squid on a separate server with a
> static IP to forward-proxy requests from Heroku to the external
> service. That way, the external service always sees the proxy server's
> static IP, instead of the Heroku service's dynamic IP.
>
> Since my proxy server can't rely on an IP address for authentication

You mean authorization, not authentication. A number (IP address) cannot
own credentials, only an entity can have credentials and credentials are
required for authentication.

> (that's the problem to begin with!), it must rely on a username and
> password. Further, the username and password cannot be transmitted in
> clear text,

Meaning: avoid Basic authentication type.

> because if an attacker were to intercept that clear text,
> then they could connect to my proxy pretending to be me, make outbound
> requests using my proxy's static IP, and thus evade the external web
> service's firewall.

Squid is not limited to the Basic authentication protocol. I see you are
already using Digest authentication, which already does what you want
even in unencrypted HTTP.

>
> Therefore, the Squid proxy must only accept connections over HTTPS,
> not HTTP. (The connection to the external web service might be HTTP or
> HTTPS.)

No. Given you already use Digest auth the SSL layer is not necessary to
prevent that attack type. It is just an extra layer to obscure the
content being transferred. I think it is a good idea to use it of
possible, but am aware there are some big troubles (namely that modern
browsers still do not support connecting to a proxy over SSL/TLS).

>
> I'm running Squid 3.1.10 on CentOS 6.5.x,

Please try an upgrade. You can find details about newer versions for
CentOS at http://wiki.squid-cache.org/KnowledgeBase/CentOS
<snip>
>
> Using this setup, HTTP proxying works fine, but HTTPS proxying does
> not.
>
> Here's an HTTP proxy request from a local box:
>
> $ curl --proxy http://my-proxy-server.example:3128 \
> --proxy-anyauth --proxy-user redacted:redacted -w '\n' \
> http://urlecho.appspot.com/echo?body=OK
> OK
>
<snip>
>
> Here's another request, this time with HTTPS:
>
> $ curl --proxy https://my-proxy-server.example:3129 \
> --proxy-anyauth --proxy-user redacted:redacted -w '\n' \
> http://urlecho.appspot.com/echo?body=OK
>
> curl: (56) Recv failure: Connection reset by peer
>
> Nothing in `access.log` after this one, but in `cache.log`:
>
> 2014/01/20 20:46:15| clientNegotiateSSL: Error negotiating SSL
> connection on FD 10: error:1407609C:SSL
> routines:SSL23_GET_CLIENT_HELLO:http request (1/-1)
>

See the serverfault response. curl is connecting to the proxy using
plain-text instead of SSL.

> Here's the above again, more verbosely:
>
> $ curl -v --proxy https://my-proxy-server.example:3129 \
> --proxy-anyauth --proxy-user redacted:redacted -w '\n' \
> http://urlecho.appspot.com/echo?body=OK
> * Adding handle: conn: 0x7f9a30804000
> * Adding handle: send: 0
> * Adding handle: recv: 0
> * Curl_addHandleToPipeline: length: 1
> * - Conn 0 (0x7f9a30804000) send_pipe: 1, recv_pipe: 0
> * About to connect() to proxy my-proxy-server.example port 3129
> (#0)
> * Trying proxy.server.IP.redacted...
> * Connected to my-proxy-server.example (proxy.server.IP.redacted)
> port 3129 (#0)

Note the absence of any mention about SSL/TLS here.

> > GET http://urlecho.appspot.com/echo?body=OK HTTP/1.1
> > User-Agent: curl/7.30.0
> > Host: urlecho.appspot.com
> > Accept: */*
> > Proxy-Connection: Keep-Alive
> >
> * Recv failure: Connection reset by peer
> * Closing connection 0
>
> curl: (56) Recv failure: Connection reset by peer
>
> Looks like an SSL error.

It is. Try using --ssl option for curl. You will also need
--proxy-digest to get the Digest auth against the proxy working for
curl.

> However, I'm reusing a subdomain-wildcard SSL
> certificate, shown in the above config as `cert.pem` and `key.pem`,
> that I've successfully deployed on other web servers. Moreover,
> accessing the proxy server directly with curl works, or at least
> establishes a connection past the SSL stage:
>
> $ curl https://my-proxy-server.example:3129
> <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN"
> "http://www.w3.org/TR/html4/strict.dtd">
>
> [--SNIP--]

This tells us that the test machine can access the web serve. Please run
the same test directly on the squid machine. That will tell whether or
not connectivity for Squid is working properly.

>
> Any ideas what I'm doing wrong? Is what I'm attempting even possible?

It is possible and being done already by some. Although to get the
broken browsers to work properly a VPN/stunnel from the client machine
to proxy port is often needed.

Amos
Received on Tue Jan 21 2014 - 21:29:15 MST