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.

Author: rousskov

docs/curl.1

@@ -1468,18 +1468,69 @@ the default authentication method curl uses with proxies.
 .IP "--proxy-digest"
 Tells curl to use HTTP Digest authentication when communicating with the given
 proxy. Use \fI--digest\fP for enabling HTTP Digest with a remote host.
+.IP "--proxy-cacert <CA certificate>"
+(SSL) Same as --cacert but used in HTTPS proxy context.
+(Added in 7.XXX)
+.IP "--proxy-capath <CA certificate directory>"
+(SSL) Same as --capath but used in HTTPS proxy context.
+(Added in 7.XXX)
+.IP "--proxy-cert <certificate[:password]>"
+(SSL) Same as \fI--cert\fP but used in HTTPS proxy context.
+(Added in 7.XXX)
+.IP "--proxy-cert-type <type>"
+(SSL) Same as \fI--cert-type\fP but used in HTTPS proxy context.
+(Added in 7.XXX)
+.IP "--proxy-ciphers <list of ciphers>"
+(SSL) Same as \fI--ciphers\fP but used in HTTPS proxy context.
+(Added in 7.XXX)
+.IP "--proxy-crlfile <file>"
+(HTTPS) Same as \fI--crlfile\fP but used in HTTPS proxy context.
+(Added in 7.XXX)
+.IP "--proxy-insecure"
+(SSL) Same as \fI--insecure\fP but used in HTTPS proxy context.
+(Added in 7.XXX)
+.IP "--proxy-key <key>"
+(SSL) Same as \fI--key\fP but used in HTTPS proxy context.
+(Added in 7.XXX)
+.IP "--proxy-key-type <type>"
+(SSL) Same as \fI--key-type\fP but used in HTTPS proxy context.
+(Added in 7.XXX)
 .IP "--proxy-negotiate"
 Tells curl to use HTTP Negotiate (SPNEGO) authentication when communicating
 with the given proxy. Use \fI--negotiate\fP for enabling HTTP Negotiate (SPNEGO)
 with a remote host. (Added in 7.17.1)
 .IP "--proxy-ntlm"
 Tells curl to use HTTP NTLM authentication when communicating with the given
 proxy. Use \fI--ntlm\fP for enabling NTLM with a remote host.
+.IP "--proxy-pass <phrase>"
+(SSL) Same as \fI--pass\fP but used in HTTPS proxy context.
+(Added in 7.XXX)
 .IP "--proxy-service-name <servicename>"
 This option allows you to change the service name for proxy negotiation.
 
 Examples: --proxy-negotiate proxy-name \fI--proxy-service-name\fP sockd would use
 sockd/proxy-name.  (Added in 7.43.0).
+.IP "--proxy-ssl-allow-beast"
+(SSL) Same as \fI--ssl-allow-beast\fP but used in HTTPS proxy context.
+(Added in 7.XXX)
+.IP "--proxy-sslv2"
+(SSL) Same as \fI--sslv2\fP but used in HTTPS proxy context.
+(Added in 7.XXX)
+.IP "--proxy-sslv3"
+(SSL) Same as \fI--sslv3\fP but used in HTTPS proxy context.
+(Added in 7.XXX)
+.IP "--proxy-tlsauthtype <authtype>"
+Same as \fI--tlsauthtype\fP but used in HTTPS proxy context.
+(Added in 7.XXX)
+.IP "--proxy-tlspassword <password>"
+Same as \fI--tlspassword\fP but used in HTTPS proxy context.
+(Added in 7.XXX)
+.IP "--proxy-tlsuser <user>"
+Same as \fI--tlsuser\fP but used in HTTPS proxy context.
+(Added in 7.XXX)
+.IP "--proxy-tlsv1"
+(SSL) Same as \fI--tlsv1\fP but used in HTTPS proxy context.
+(Added in 7.XXX)
 .IP "--proxy1.0 <proxyhost[:port]>"
 Use the specified HTTP 1.0 proxy. If the port number is not specified, it is
 assumed at port 1080.

docs/libcurl/curl_easy_getinfo.3

@@ -104,6 +104,9 @@ See \fICURLINFO_REQUEST_SIZE(3)\fP
 .IP CURLINFO_SSL_VERIFYRESULT
 Certificate verification result.
 See \fICURLINFO_SSL_VERIFYRESULT(3)\fP
+.IP CURLINFO_PROXY_SSL_VERIFYRESULT
+Proxy certificate verification result.
+See \fICURLINFO_PROXY_SSL_VERIFYRESULT(3)\fP
 .IP CURLINFO_SSL_ENGINES
 A list of OpenSSL crypto engines.
 See \fICURLINFO_SSL_ENGINES(3)\fP

docs/libcurl/curl_easy_setopt.3

@@ -159,10 +159,14 @@ Protocols to allow redirects to. See \fICURLOPT_REDIR_PROTOCOLS(3)\fP
 Default protocol. See \fICURLOPT_DEFAULT_PROTOCOL(3)\fP
 .IP CURLOPT_PROXY
 Proxy to use. See \fICURLOPT_PROXY(3)\fP
+.IP CURLOPT_SOCKS_PROXY
+Socks proxy to use. See \fICURLOPT_SOCKS_PROXY(3)\fP
 .IP CURLOPT_PROXYPORT
 Proxy port to use. See \fICURLOPT_PROXYPORT(3)\fP
 .IP CURLOPT_PROXYTYPE
 Proxy type. See \fICURLOPT_PROXYTYPE(3)\fP
+.IP CURLOPT_SOCKS_PROXYTYPE
+Socks proxy type. See \fICURLOPT_SOCKS_PROXYTYPE(3)\fP
 .IP CURLOPT_NOPROXY
 Filter out hosts from proxy use. \fICURLOPT_NOPROXY(3)\fP
 .IP CURLOPT_HTTPPROXYTUNNEL
@@ -228,10 +232,16 @@ Proxy password. See \fICURLOPT_PROXYPASSWORD(3)\fP
 HTTP server authentication methods. See \fICURLOPT_HTTPAUTH(3)\fP
 .IP CURLOPT_TLSAUTH_USERNAME
 TLS authentication user name. See \fICURLOPT_TLSAUTH_USERNAME(3)\fP
+.IP CURLOPT_PROXY_TLSAUTH_USERNAME
+Proxy TLS authentication user name. See \fICURLOPT_PROXY_TLSAUTH_USERNAME(3)\fP
 .IP CURLOPT_TLSAUTH_PASSWORD
 TLS authentication password. See \fICURLOPT_TLSAUTH_PASSWORD(3)\fP
+.IP CURLOPT_PROXY_TLSAUTH_PASSWORD
+Proxy TLS authentication password. See \fICURLOPT_PROXY_TLSAUTH_PASSWORD(3)\fP
 .IP CURLOPT_TLSAUTH_TYPE
 TLS authentication methods. See \fICURLOPT_TLSAUTH_TYPE(3)\fP
+.IP CURLOPT_PROXY_TLSAUTH_TYPE
+Proxy TLS authentication methods. See \fICURLOPT_PROXY_TLSAUTH_TYPE(3)\fP
 .IP CURLOPT_PROXYAUTH
 HTTP proxy authentication methods. See \fICURLOPT_PROXYAUTH(3)\fP
 .IP CURLOPT_SASL_IR
@@ -447,14 +457,24 @@ Timeout for waiting for the server's connect back to be accepted. See \fICURLOPT
 .SH SSL and SECURITY OPTIONS
 .IP CURLOPT_SSLCERT
 Client cert. See \fICURLOPT_SSLCERT(3)\fP
+.IP CURLOPT_PROXY_SSLCERT
+Proxy client cert. See \fICURLOPT_PROXY_SSLCERT(3)\fP
 .IP CURLOPT_SSLCERTTYPE
 Client cert type.  See \fICURLOPT_SSLCERTTYPE(3)\fP
+.IP CURLOPT_PROXY_SSLCERTTYPE
+Proxy client cert type.  See \fICURLOPT_PROXY_SSLCERTTYPE(3)\fP
 .IP CURLOPT_SSLKEY
 Client key. See \fICURLOPT_SSLKEY(3)\fP
+.IP CURLOPT_PROXY_SSLKEY
+Proxy client key. See \fICURLOPT_PROXY_SSLKEY(3)\fP
 .IP CURLOPT_SSLKEYTYPE
 Client key type. See \fICURLOPT_SSLKEYTYPE(3)\fP
+.IP CURLOPT_PROXY_SSLKEYTYPE
+Proxy client key type. See \fICURLOPT_PROXY_SSLKEYTYPE(3)\fP
 .IP CURLOPT_KEYPASSWD
 Client key password. See \fICURLOPT_KEYPASSWD(3)\fP
+.IP CURLOPT_PROXY_KEYPASSWD
+Proxy client key password. See \fICURLOPT_PROXY_KEYPASSWD(3)\fP
 .IP CURLOPT_SSL_ENABLE_ALPN
 Enable use of ALPN. See \fICURLOPT_SSL_ENABLE_ALPN(3)\fP
 .IP CURLOPT_SSL_ENABLE_NPN
@@ -467,20 +487,32 @@ Default SSL engine. See \fICURLOPT_SSLENGINE_DEFAULT(3)\fP
 Enable TLS False Start. See \fICURLOPT_SSL_FALSESTART(3)\fP
 .IP CURLOPT_SSLVERSION
 SSL version to use. See \fICURLOPT_SSLVERSION(3)\fP
+.IP CURLOPT_PROXY_SSLVERSION
+Proxy SSL version to use. See \fICURLOPT_PROXY_SSLVERSION(3)\fP
 .IP CURLOPT_SSL_VERIFYHOST
 Verify the host name in the SSL certificate. See \fICURLOPT_SSL_VERIFYHOST(3)\fP
+.IP CURLOPT_PROXY_SSL_VERIFYHOST
+Verify the host name in the proxy SSL certificate. See \fICURLOPT_PROXY_SSL_VERIFYHOST(3)\fP
 .IP CURLOPT_SSL_VERIFYPEER
 Verify the SSL certificate. See \fICURLOPT_SSL_VERIFYPEER(3)\fP
+.IP CURLOPT_PROXY_SSL_VERIFYPEER
+Verify the proxy SSL certificate. See \fICURLOPT_PROXY_SSL_VERIFYPEER(3)\fP
 .IP CURLOPT_SSL_VERIFYSTATUS
 Verify the SSL certificate's status. See \fICURLOPT_SSL_VERIFYSTATUS(3)\fP
 .IP CURLOPT_CAINFO
 CA cert bundle. See \fICURLOPT_CAINFO(3)\fP
+.IP CURLOPT_PROXY_CAINFO
+Proxy CA cert bundle. See \fICURLOPT_PROXY_CAINFO(3)\fP
 .IP CURLOPT_ISSUERCERT
 Issuer certificate. See \fICURLOPT_ISSUERCERT(3)\fP
 .IP CURLOPT_CAPATH
 Path to CA cert bundle. See \fICURLOPT_CAPATH(3)\fP
+.IP CURLOPT_PROXY_CAPATH
+Path to proxy CA cert bundle. See \fICURLOPT_PROXY_CAPATH(3)\fP
 .IP CURLOPT_CRLFILE
 Certificate Revocation List. See \fICURLOPT_CRLFILE(3)\fP
+.IP CURLOPT_PROXY_CRLFILE
+Proxy Certificate Revocation List. See \fICURLOPT_PROXY_CRLFILE(3)\fP
 .IP CURLOPT_CERTINFO
 Extract certificate info. See \fICURLOPT_CERTINFO(3)\fP
 .IP CURLOPT_PINNEDPUBLICKEY
@@ -491,10 +523,14 @@ Provide source for entropy random data. See \fICURLOPT_RANDOM_FILE(3)\fP
 Identify EGD socket for entropy. See \fICURLOPT_EGDSOCKET(3)\fP
 .IP CURLOPT_SSL_CIPHER_LIST
 Ciphers to use. See \fICURLOPT_SSL_CIPHER_LIST(3)\fP
+.IP CURLOPT_PROXY_SSL_CIPHER_LIST
+Proxy ciphers to use. See \fICURLOPT_PROXY_SSL_CIPHER_LIST(3)\fP
 .IP CURLOPT_SSL_SESSIONID_CACHE
 Disable SSL session-id cache. See \fICURLOPT_SSL_SESSIONID_CACHE(3)\fP
 .IP CURLOPT_SSL_OPTIONS
 Control SSL behavior. See \fICURLOPT_SSL_OPTIONS(3)\fP
+.IP CURLOPT_PROXY_SSL_OPTIONS
+Control proxy SSL behavior. See \fICURLOPT_PROXY_SSL_OPTIONS(3)\fP
 .IP CURLOPT_KRBLEVEL
 Kerberos security level. See \fICURLOPT_KRBLEVEL(3)\fP
 .IP CURLOPT_GSSAPI_DELEGATION

docs/libcurl/opts/CURLINFO_PROXY_SSL_VERIFYRESULT.3

@@ -0,0 +1,44 @@
+.\" **************************************************************************
+.\" *                                  _   _ ____  _
+.\" *  Project                     ___| | | |  _ \| |
+.\" *                             / __| | | | |_) | |
+.\" *                            | (__| |_| |  _ <| |___
+.\" *                             \___|\___/|_| \_\_____|
+.\" *
+.\" * Copyright (C) 1998 - 2016, Daniel Stenberg, <daniel@haxx.se>, et al.
+.\" *
+.\" * This software is licensed as described in the file COPYING, which
+.\" * you should have received as part of this distribution. The terms
+.\" * are also available at https://curl.haxx.se/docs/copyright.html.
+.\" *
+.\" * You may opt to use, copy, modify, merge, publish, distribute and/or sell
+.\" * copies of the Software, and permit persons to whom the Software is
+.\" * furnished to do so, under the terms of the COPYING file.
+.\" *
+.\" * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+.\" * KIND, either express or implied.
+.\" *
+.\" **************************************************************************
+.\"
+.TH CURLINFO_PROXY_SSL_VERIFYRESULT 3 "16 Nov 2016" "libcurl 7.51.1" "curl_easy_getinfo options"
+.SH NAME
+CURLINFO_PROXY_SSL_VERIFYRESULT \- get the result of the proxy certification verification
+.SH SYNOPSIS
+#include <curl/curl.h>
+
+CURLcode curl_easy_getinfo(CURL *handle, CURLINFO_PROXY_SSL_VERIFYRESULT, long *result);
+.SH DESCRIPTION
+TODO: Make this text specific to HTTPS proxy. (Added in 7.XXX)
+Pass a pointer to a long to receive the result of the certification
+verification that was requested (using the \fICURLOPT_SSL_VERIFYPEER(3)\fP
+option.
+.SH PROTOCOLS
+All using TLS
+.SH EXAMPLE
+TODO
+.SH AVAILABILITY
+Added in 7.5
+.SH RETURN VALUE
+Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.
+.SH "SEE ALSO"
+.BR curl_easy_getinfo "(3), " curl_easy_setopt "(3), "

docs/libcurl/opts/CURLOPT_PROXY_CAINFO.3

@@ -0,0 +1,64 @@
+.\" **************************************************************************
+.\" *                                  _   _ ____  _
+.\" *  Project                     ___| | | |  _ \| |
+.\" *                             / __| | | | |_) | |
+.\" *                            | (__| |_| |  _ <| |___
+.\" *                             \___|\___/|_| \_\_____|
+.\" *
+.\" * Copyright (C) 1998 - 2016, Daniel Stenberg, <daniel@haxx.se>, et al.
+.\" *
+.\" * This software is licensed as described in the file COPYING, which
+.\" * you should have received as part of this distribution. The terms
+.\" * are also available at https://curl.haxx.se/docs/copyright.html.
+.\" *
+.\" * You may opt to use, copy, modify, merge, publish, distribute and/or sell
+.\" * copies of the Software, and permit persons to whom the Software is
+.\" * furnished to do so, under the terms of the COPYING file.
+.\" *
+.\" * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+.\" * KIND, either express or implied.
+.\" *
+.\" **************************************************************************
+.\"
+.TH CURLOPT_PROXY_CAINFO 3 "16 Nov 2016" "libcurl 7.51.1" "curl_easy_setopt options"
+.SH NAME
+CURLOPT_PROXY_CAINFO \- path to proxy Certificate Authority (CA) bundle
+.SH SYNOPSIS
+#include <curl/curl.h>
+
+CURLcode curl_easy_setopt(CURL *handle, CURLOPT_PROXY_CAINFO, char *path);
+.SH DESCRIPTION
+TODO: Make this text specific to HTTPS proxy. (Added in 7.XXX)
+Pass a char * to a zero terminated string naming a file holding one or more
+certificates to verify the peer with.
+
+If \fICURLOPT_SSL_VERIFYPEER(3)\fP is zero and you avoid verifying the
+server's certificate, \fICURLOPT_CAINFO(3)\fP need not even indicate an
+accessible file.
+
+This option is by default set to the system path where libcurl's cacert bundle
+is assumed to be stored, as established at build time.
+
+If curl is built against the NSS SSL library, the NSS PEM PKCS#11 module
+(libnsspem.so) needs to be available for this option to work properly.
+
+(iOS and macOS only) If curl is built against Secure Transport, then this
+option is supported for backward compatibility with other SSL engines, but it
+should not be set. If the option is not set, then curl will use the
+certificates in the system and user Keychain to verify the peer, which is the
+preferred method of verifying the peer's certificate chain.
+.SH DEFAULT
+Built-in system specific
+.SH PROTOCOLS
+All TLS based protocols: HTTPS, FTPS, IMAPS, POP3S, SMTPS etc.
+.SH EXAMPLE
+TODO
+.SH AVAILABILITY
+For SSL engines that don't support certificate files the CURLOPT_PROXY_CAINFO option
+is ignored. Refer to https://curl.haxx.se/docs/ssl-compared.html
+.SH RETURN VALUE
+Returns CURLE_OK if the option is supported, CURLE_UNKNOWN_OPTION if not, or
+CURLE_OUT_OF_MEMORY if there was insufficient heap space.
+.SH "SEE ALSO"
+.BR CURLOPT_CAPATH "(3), "
+.BR CURLOPT_SSL_VERIFYPEER "(3), " CURLOPT_SSL_VERIFYHOST "(3), "

docs/libcurl/opts/CURLOPT_PROXY_CAPATH.3

@@ -0,0 +1,54 @@
+.\" **************************************************************************
+.\" *                                  _   _ ____  _
+.\" *  Project                     ___| | | |  _ \| |
+.\" *                             / __| | | | |_) | |
+.\" *                            | (__| |_| |  _ <| |___
+.\" *                             \___|\___/|_| \_\_____|
+.\" *
+.\" * Copyright (C) 1998 - 2016, Daniel Stenberg, <daniel@haxx.se>, et al.
+.\" *
+.\" * This software is licensed as described in the file COPYING, which
+.\" * you should have received as part of this distribution. The terms
+.\" * are also available at https://curl.haxx.se/docs/copyright.html.
+.\" *
+.\" * You may opt to use, copy, modify, merge, publish, distribute and/or sell
+.\" * copies of the Software, and permit persons to whom the Software is
+.\" * furnished to do so, under the terms of the COPYING file.
+.\" *
+.\" * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+.\" * KIND, either express or implied.
+.\" *
+.\" **************************************************************************
+.\"
+.TH CURLOPT_PROXY_CAPATH 3 "16 Nov 2016" "libcurl 7.51.1" "curl_easy_setopt options"
+.SH NAME
+CURLOPT_PROXY_CAPATH \- specify directory holding proxy CA certificates
+.SH SYNOPSIS
+#include <curl/curl.h>
+
+CURLcode curl_easy_setopt(CURL *handle, CURLOPT_PROXY_CAPATH, char *capath);
+.SH DESCRIPTION
+TODO: Make this text specific to HTTPS proxy. (Added in 7.XXX)
+Pass a char * to a zero terminated string naming a directory holding multiple
+CA certificates to verify the peer with. If libcurl is built against OpenSSL,
+the certificate directory must be prepared using the openssl c_rehash utility.
+This makes sense only when used in combination with the
+\fICURLOPT_SSL_VERIFYPEER(3)\fP option.
+
+The \fICURLOPT_CAPATH(3)\fP function apparently does not work in Windows due
+to some limitation in openssl.
+.SH DEFAULT
+NULL
+.SH PROTOCOLS
+All TLS based protocols: HTTPS, FTPS, IMAPS, POP3S, SMTPS etc.
+.SH EXAMPLE
+TODO
+.SH AVAILABILITY
+This option is supported by the OpenSSL, GnuTLS and PolarSSL backends. The NSS
+backend provides the option only for backward compatibility.
+.SH RETURN VALUE
+Returns CURLE_OK if TLS enabled, and CURLE_UNKNOWN_OPTION if not, or
+CURLE_OUT_OF_MEMORY if there was insufficient heap space.
+.SH "SEE ALSO"
+.BR CURLOPT_CAINFO "(3), "
+.BR CURLOPT_STDERR "(3), " CURLOPT_DEBUGFUNCTION "(3), "