http: use credential API to handle proxy authentication

Currently, the only way to pass proxy credentials to curl is by including them
in the proxy URL. Usually, this means they will end up on disk unencrypted, one
way or another (by inclusion in ~/.gitconfig, shell profile or history). Since
proxy authentication often uses a domain user, credentials can be security
sensitive; therefore, a safer way of passing credentials is desirable.

If the configured proxy contains a username but not a password, query the
credential API for one. Also, make sure we approve/reject proxy credentials
properly.

For consistency reasons, add parsing of http_proxy/https_proxy/all_proxy
environment variables, which would otherwise be evaluated as a fallback by curl.
Without this, we would have different semantics for git configuration and
environment variables.

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

Documentation/config.txt

@@ -1596,9 +1596,13 @@ help.htmlPath::
 
 http.proxy::
 	Override the HTTP proxy, normally configured using the 'http_proxy',
-	'https_proxy', and 'all_proxy' environment variables (see
-	`curl(1)`).  This can be overridden on a per-remote basis; see
-	remote.<name>.proxy
+	'https_proxy', and 'all_proxy' environment variables (see `curl(1)`). In
+	addition to the syntax understood by curl, it is possible to specify a
+	proxy string with a user name but no password, in which case git will
+	attempt to acquire one in the same way it does for other credentials. See
+	linkgit:gitcredentials[7] for more information. The syntax thus is
+	'[protocol://][user[:password]@]proxyhost[:port]'. 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

http.c

@@ -80,6 +80,8 @@ static struct {
 	 * here, too
 	 */
 };
+static struct credential proxy_auth = CREDENTIAL_INIT;
+static const char *curl_proxyuserpwd;
 static const char *curl_cookie_file;
 static int curl_save_cookies;
 struct credential http_auth = CREDENTIAL_INIT;
@@ -177,6 +179,9 @@ static void finish_active_slot(struct active_request_slot *slot)
 #else
 		slot->results->auth_avail = 0;
 #endif
+
+		curl_easy_getinfo(slot->curl, CURLINFO_HTTP_CONNECTCODE,
+			&slot->results->http_connectcode);
 	}
 
 	/* Run callback if appropriate */
@@ -334,8 +339,32 @@ static void var_override(const char **var, char *value)
 	}
 }
 
+static void set_proxyauth_name_password(CURL *result)
+{
+#if LIBCURL_VERSION_NUM >= 0x071301
+		curl_easy_setopt(result, CURLOPT_PROXYUSERNAME,
+			proxy_auth.username);
+		curl_easy_setopt(result, CURLOPT_PROXYPASSWORD,
+			proxy_auth.password);
+#else
+		struct strbuf s = STRBUF_INIT;
+
+		strbuf_addstr_urlencode(&s, proxy_auth.username, 1);
+		strbuf_addch(&s, ':');
+		strbuf_addstr_urlencode(&s, proxy_auth.password, 1);
+		curl_proxyuserpwd = strbuf_detach(&s, NULL);
+		curl_easy_setopt(result, CURLOPT_PROXYUSERPWD, curl_proxyuserpwd);
+#endif
+}
+
 static void init_curl_proxy_auth(CURL *result)
 {
+	if (proxy_auth.username) {
+		if (!proxy_auth.password)
+			credential_fill(&proxy_auth);
+		set_proxyauth_name_password(result);
+	}
+
 	var_override(&http_proxy_authmethod, getenv("GIT_HTTP_PROXY_AUTHMETHOD"));
 
 #if LIBCURL_VERSION_NUM >= 0x070a07 /* CURLOPT_PROXYAUTH and CURLAUTH_ANY */
@@ -517,6 +546,31 @@ static CURL *get_curl_handle(void)
 		curl_easy_setopt(result, CURLOPT_USE_SSL, CURLUSESSL_TRY);
 #endif
 
+	/*
+	 * CURL also examines these variables as a fallback; but we need to query
+	 * them here in order to decide whether to prompt for missing password (cf.
+	 * init_curl_proxy_auth()).
+	 *
+	 * Unlike many other common environment variables, these are historically
+	 * lowercase only. It appears that CURL did not know this and implemented
+	 * only uppercase variants, which was later corrected to take both - with
+	 * the exception of http_proxy, which is lowercase only also in CURL. As
+	 * the lowercase versions are the historical quasi-standard, they take
+	 * precedence here, as in CURL.
+	 */
+	if (!curl_http_proxy) {
+		if (!strcmp(http_auth.protocol, "https")) {
+			var_override(&curl_http_proxy, getenv("HTTPS_PROXY"));
+			var_override(&curl_http_proxy, getenv("https_proxy"));
+		} else {
+			var_override(&curl_http_proxy, getenv("http_proxy"));
+		}
+		if (!curl_http_proxy) {
+			var_override(&curl_http_proxy, getenv("ALL_PROXY"));
+			var_override(&curl_http_proxy, getenv("all_proxy"));
+		}
+	}
+
 	if (curl_http_proxy) {
 		curl_easy_setopt(result, CURLOPT_PROXY, curl_http_proxy);
 #if LIBCURL_VERSION_NUM >= 0x071800
@@ -530,6 +584,16 @@ static CURL *get_curl_handle(void)
 			curl_easy_setopt(result,
 				CURLOPT_PROXYTYPE, CURLPROXY_SOCKS4);
 #endif
+		if (strstr(curl_http_proxy, "://"))
+			credential_from_url(&proxy_auth, curl_http_proxy);
+		else {
+			struct strbuf url = STRBUF_INIT;
+			strbuf_addf(&url, "http://%s", curl_http_proxy);
+			credential_from_url(&proxy_auth, url.buf);
+			strbuf_release(&url);
+		}
+
+		curl_easy_setopt(result, CURLOPT_PROXY, proxy_auth.host);
 	}
 	init_curl_proxy_auth(result);
 
@@ -673,6 +737,15 @@ void http_cleanup(void)
 		curl_http_proxy = NULL;
 	}
 
+	if (proxy_auth.password) {
+		memset(proxy_auth.password, 0, strlen(proxy_auth.password));
+		free(proxy_auth.password);
+		proxy_auth.password = NULL;
+	}
+
+	free((void *)curl_proxyuserpwd);
+	curl_proxyuserpwd = NULL;
+
 	free((void *)http_proxy_authmethod);
 	http_proxy_authmethod = NULL;
 
@@ -1005,6 +1078,8 @@ static int handle_curl_result(struct slot_results *results)
 
 	if (results->curl_result == CURLE_OK) {
 		credential_approve(&http_auth);
+		if (proxy_auth.password)
+			credential_approve(&proxy_auth);
 		return HTTP_OK;
 	} else if (missing_target(results))
 		return HTTP_MISSING_TARGET;
@@ -1019,6 +1094,8 @@ static int handle_curl_result(struct slot_results *results)
 			return HTTP_REAUTH;
 		}
 	} else {
+		if (results->http_connectcode == 407)
+			credential_reject(&proxy_auth);
 #if LIBCURL_VERSION_NUM >= 0x070c00
 		if (!curl_errorstr[0])
 			strlcpy(curl_errorstr,

http.h

@@ -54,6 +54,7 @@ struct slot_results {
 	CURLcode curl_result;
 	long http_code;
 	long auth_avail;
+	long http_connectcode;
 };
 
 struct active_request_slot {