http: allow selection of proxy authentication method

CURLAUTH_ANY does not work with proxies which answer unauthenticated requests
with a 307 redirect to an error page instead of a 407 listing supported
authentication methods. Therefore, allow the authentication method to be set
using the environment variable GIT_HTTP_PROXY_AUTHMETHOD or configuration
variables http.proxyAuthmethod and remote.<name>.proxyAuthmethod (in analogy
to http.proxy and remote.<name>.proxy).

The following values are supported:

* anyauth (default)
* basic
* digest
* negotiate
* ntlm

Signed-off-by: Knut Franke <k.franke@science-computing.de>
Signed-off-by: Elia Pinto <gitter.spiros@gmail.com>
Helped-by: Junio C Hamano <gitster@pobox.com>
Helped-by: Eric Sunshine <sunshine@sunshineco.com>
Helped-by: Elia Pinto <gitter.spiros@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config.txt

@@ -1600,6 +1600,27 @@ http.proxy::
 	`curl(1)`).  This can be overridden on a per-remote basis; see
 	remote.<name>.proxy
 
+http.proxyAuthMethod::
+	Set the method with which to authenticate against the HTTP proxy. This
+	only takes effect if the configured proxy string contains a user name part
+	(i.e. is of the form 'user@host' or 'user@host:port'). This can be
+	overridden on a per-remote basis; see `remote.<name>.proxyAuthMethod`.
+	Both can be overridden by the 'GIT_HTTP_PROXY_AUTHMETHOD' environment
+	variable.  Possible values are:
++
+--
+* `anyauth` - Automatically pick a suitable authentication method. It is
+  assumed that the proxy answers an unauthenticated request with a 407
+  status code and one or more Proxy-authenticate headers with supported
+  authentication methods. This is the default.
+* `basic` - HTTP Basic authentication
+* `digest` - HTTP Digest authentication; this prevents the password from being
+  transmitted to the proxy in clear text
+* `negotiate` - GSS-Negotiate authentication (compare the --negotiate option
+  of `curl(1)`)
+* `ntlm` - NTLM authentication (compare the --ntlm option of `curl(1)`)
+--
+
 http.cookieFile::
 	File containing previously stored cookie lines which should be used
 	in the Git http session, if they match the server. The file format
@@ -2407,6 +2428,11 @@ remote.<name>.proxy::
 	the proxy to use for that remote.  Set to the empty string to
 	disable proxying for that remote.
 
+remote.<name>.proxyAuthMethod::
+	For remotes that require curl (http, https and ftp), the method to use for
+	authenticating against the proxy in use (probably set in
+	`remote.<name>.proxy`). See `http.proxyAuthMethod`.
+
 remote.<name>.fetch::
 	The default set of "refspec" for linkgit:git-fetch[1]. See
 	linkgit:git-fetch[1].

Documentation/technical/api-remote.txt

@@ -51,6 +51,10 @@ struct remote
 
 	The proxy to use for curl (http, https, ftp, etc.) URLs.
 
+`http_proxy_authmethod`::
+
+	The method used for authenticating against `http_proxy`.
+
 struct remotes can be found by name with remote_get(), and iterated
 through with for_each_remote(). remote_get(NULL) will return the
 default remote, given the current branch and configuration.

http.c

@@ -62,6 +62,24 @@ static long curl_low_speed_limit = -1;
 static long curl_low_speed_time = -1;
 static int curl_ftp_no_epsv;
 static const char *curl_http_proxy;
+static const char *http_proxy_authmethod;
+static struct {
+	const char *name;
+	long curlauth_param;
+} proxy_authmethods[] = {
+	{ "basic", CURLAUTH_BASIC },
+	{ "digest", CURLAUTH_DIGEST },
+	{ "negotiate", CURLAUTH_GSSNEGOTIATE },
+	{ "ntlm", CURLAUTH_NTLM },
+#ifdef LIBCURL_CAN_HANDLE_AUTH_ANY
+	{ "anyauth", CURLAUTH_ANY },
+#endif
+	/*
+	 * CURLAUTH_DIGEST_IE has no corresponding command-line option in
+	 * curl(1) and is not included in CURLAUTH_ANY, so we leave it out
+	 * here, too
+	 */
+};
 static const char *curl_cookie_file;
 static int curl_save_cookies;
 struct credential http_auth = CREDENTIAL_INIT;
@@ -256,6 +274,9 @@ static int http_options(const char *var, const char *value, void *cb)
 	if (!strcmp("http.proxy", var))
 		return git_config_string(&curl_http_proxy, var, value);
 
+	if (!strcmp("http.proxyauthmethod", var))
+		return git_config_string(&http_proxy_authmethod, var, value);
+
 	if (!strcmp("http.cookiefile", var))
 		return git_config_string(&curl_cookie_file, var, value);
 	if (!strcmp("http.savecookies", var)) {
@@ -304,6 +325,40 @@ static void init_curl_http_auth(CURL *result)
 #endif
 }
 
+/* *var must be free-able */
+static void var_override(const char **var, char *value)
+{
+	if (value) {
+		free((void *)*var);
+		*var = xstrdup(value);
+	}
+}
+
+static void init_curl_proxy_auth(CURL *result)
+{
+	var_override(&http_proxy_authmethod, getenv("GIT_HTTP_PROXY_AUTHMETHOD"));
+
+#if LIBCURL_VERSION_NUM >= 0x070a07 /* CURLOPT_PROXYAUTH and CURLAUTH_ANY */
+	if (http_proxy_authmethod) {
+		int i;
+		for (i = 0; i < ARRAY_SIZE(proxy_authmethods); i++) {
+			if (!strcmp(http_proxy_authmethod, proxy_authmethods[i].name)) {
+				curl_easy_setopt(result, CURLOPT_PROXYAUTH,
+						proxy_authmethods[i].curlauth_param);
+				break;
+			}
+		}
+		if (i == ARRAY_SIZE(proxy_authmethods)) {
+			warning("unsupported proxy authentication method %s: using anyauth",
+					http_proxy_authmethod);
+			curl_easy_setopt(result, CURLOPT_PROXYAUTH, CURLAUTH_ANY);
+		}
+	}
+	else
+		curl_easy_setopt(result, CURLOPT_PROXYAUTH, CURLAUTH_ANY);
+#endif
+}
+
 static int has_cert_password(void)
 {
 	if (ssl_cert == NULL || ssl_cert_password_required != 1)
@@ -476,9 +531,7 @@ static CURL *get_curl_handle(void)
 				CURLOPT_PROXYTYPE, CURLPROXY_SOCKS4);
 #endif
 	}
-#if LIBCURL_VERSION_NUM >= 0x070a07
-	curl_easy_setopt(result, CURLOPT_PROXYAUTH, CURLAUTH_ANY);
-#endif
+	init_curl_proxy_auth(result);
 
 	set_curl_keepalive(result);
 
@@ -519,6 +572,9 @@ void http_init(struct remote *remote, const char *url, int proactive_auth)
 	if (remote && remote->http_proxy)
 		curl_http_proxy = xstrdup(remote->http_proxy);
 
+	if (remote)
+		var_override(&http_proxy_authmethod, remote->http_proxy_authmethod);
+
 	pragma_header = curl_slist_append(pragma_header, "Pragma: no-cache");
 	no_pragma_header = curl_slist_append(no_pragma_header, "Pragma:");
 
@@ -617,6 +673,9 @@ void http_cleanup(void)
 		curl_http_proxy = NULL;
 	}
 
+	free((void *)http_proxy_authmethod);
+	http_proxy_authmethod = NULL;
+
 	if (cert_auth.password != NULL) {
 		memset(cert_auth.password, 0, strlen(cert_auth.password));
 		free(cert_auth.password);

remote.c

@@ -428,6 +428,9 @@ static int handle_config(const char *key, const char *value, void *cb)
 	} else if (!strcmp(subkey, ".proxy")) {
 		return git_config_string((const char **)&remote->http_proxy,
 					 key, value);
+	} else if (!strcmp(subkey, ".proxyauthmethod")) {
+		return git_config_string((const char **)&remote->http_proxy_authmethod,
+					 key, value);
 	} else if (!strcmp(subkey, ".vcs")) {
 		return git_config_string(&remote->foreign_vcs, key, value);
 	}

remote.h

@@ -54,6 +54,7 @@ struct remote {
 	 * for curl remotes only
 	 */
 	char *http_proxy;
+	char *http_proxy_authmethod;
 };
 
 struct remote *remote_get(const char *name);