proxy: Support HTTPS proxy and SOCKS+HTTP(s)

* HTTPS proxies:

An HTTPS proxy receives all transactions over an SSL/TLS connection.
Once a secure connection with the proxy is established, the user agent
uses the proxy as usual, including sending CONNECT requests to instruct
the proxy to establish a [usually secure] TCP tunnel with an origin
server. HTTPS proxies protect nearly all aspects of user-proxy
communications as opposed to HTTP proxies that receive all requests
(including CONNECT requests) in vulnerable clear text.

With HTTPS proxies, it is possible to have two concurrent _nested_
SSL/TLS sessions: the "outer" one between the user agent and the proxy
and the "inner" one between the user agent and the origin server
(through the proxy). This change adds supports for such nested sessions
as well.

A secure connection with a proxy requires its own set of the usual SSL
options (their actual descriptions differ and need polishing, see TODO):

  --proxy-cacert FILE        CA certificate to verify peer against
  --proxy-capath DIR         CA directory to verify peer against
  --proxy-cert CERT[:PASSWD] Client certificate file and password
  --proxy-cert-type TYPE     Certificate file type (DER/PEM/ENG)
  --proxy-ciphers LIST       SSL ciphers to use
  --proxy-crlfile FILE       Get a CRL list in PEM format from the file
  --proxy-insecure           Allow connections to proxies with bad certs
  --proxy-key KEY            Private key file name
  --proxy-key-type TYPE      Private key file type (DER/PEM/ENG)
  --proxy-pass PASS          Pass phrase for the private key
  --proxy-ssl-allow-beast    Allow security flaw to improve interop
  --proxy-sslv2              Use SSLv2
  --proxy-sslv3              Use SSLv3
  --proxy-tlsv1              Use TLSv1
  --proxy-tlsuser USER       TLS username
  --proxy-tlspassword STRING TLS password
  --proxy-tlsauthtype STRING TLS authentication type (default SRP)

All --proxy-foo options are independent from their --foo counterparts,
except --proxy-crlfile which defaults to --crlfile and --proxy-capath
which defaults to --capath.

Curl now also supports %{proxy_ssl_verify_result} --write-out variable,
similar to the existing %{ssl_verify_result} variable.

Supported backends: OpenSSL, GnuTLS, and NSS.

* A SOCKS proxy + HTTP/HTTPS proxy combination:

If both --socks* and --proxy options are given, Curl first connects to
the SOCKS proxy and then connects (through SOCKS) to the HTTP or HTTPS
proxy.

TODO: Update documentation for the new APIs and --proxy-* options.
Look for "Added in 7.XXX" marks.

1 files changed, 13 insertions, 3 deletions

diff --git a/lib/socks.c b/lib/socks.c
index 3b28798e5..c10543734 100644
--- a/lib/socks.c
+++ b/lib/socks.c
@@ -109,9 +109,10 @@ CURLcode Curl_SOCKS4(const char *proxy_name,
                      const char *hostname,
                      int remote_port,
                      int sockindex,
-                     struct connectdata *conn,
-                     bool protocol4a)
+                     struct connectdata *conn)
 {
+  const bool protocol4a =
+    (conn->socks_proxy.proxytype == CURLPROXY_SOCKS4A) ? TRUE : FALSE;
 #define SOCKS4REQLEN 262
   unsigned char socksreq[SOCKS4REQLEN]; /* room for SOCKS4 request incl. user
                                            id */
@@ -126,6 +127,10 @@ CURLcode Curl_SOCKS4(const char *proxy_name,
     return CURLE_OPERATION_TIMEDOUT;
   }
 
+  if(conn->bits.httpproxy)
+    infof(conn->data, "SOCKS4%s: connecting to HTTP proxy %s port %d\n",
+          protocol4a ? "a" : "", hostname, remote_port);
+
   (void)curlx_nonblock(sock, FALSE);
 
   infof(data, "SOCKS4 communication to %s:%d\n", hostname, remote_port);
@@ -377,10 +382,15 @@ CURLcode Curl_SOCKS5(const char *proxy_name,
   curl_socket_t sock = conn->sock[sockindex];
   struct Curl_easy *data = conn->data;
   time_t timeout;
-  bool socks5_resolve_local = (conn->proxytype == CURLPROXY_SOCKS5)?TRUE:FALSE;
+  bool socks5_resolve_local =
+    (conn->socks_proxy.proxytype == CURLPROXY_SOCKS5) ? TRUE : FALSE;
   const size_t hostname_len = strlen(hostname);
   ssize_t len = 0;
 
+  if(conn->bits.httpproxy)
+    infof(conn->data, "SOCKS5: connecting to HTTP proxy %s port %d\n",
+          hostname, remote_port);
+
   /* RFC1928 chapter 5 specifies max 255 chars for domain name in packet */
   if(!socks5_resolve_local && hostname_len > 255) {
     infof(conn->data, "SOCKS5: server resolving disabled for hostnames of "