http: pass http.cookiefile using CURLOPT_COOKIEFILE

If the config option http.cookiefile is set, pass this file to libCURL using
the CURLOPT_COOKIEFILE option. This is similar to calling curl with the -b
option.  This allows git http authorization with authentication mechanisms
that use cookies, such as SAML Enhanced Client or Proxy (ECP) used by
Shibboleth.

To use SAML/ECP, the user needs to request a session cookie with their own ECP
code. See for example:

<https://wiki.shibboleth.net/confluence/display/SHIB2/ECP>

Once the cookie file has been created, it can be passed to git with, e.g.

git config --global http.cookiefile "/home/dbrown/.curlcookies"

libCURL will then pass the appropriate session cookies to the git http server.

Signed-off-by: Duncan Brown <duncan.brown@ligo.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config.txt

@@ -1196,6 +1196,14 @@ http.proxy::
 	environment variable (see linkgit:curl[1]).  This can be overridden
 	on a per-remote basis; see remote.<name>.proxy
 
+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
+	of the file to read cookies from should be plain HTTP headers or
+	the Netscape/Mozilla cookie file format (see linkgit:curl[1]).
+	NOTE that the file specified with http.cookiefile is only used as
+	input. No cookies will be stored in the file.
+
 http.sslVerify::
 	Whether to verify the SSL certificate when fetching or pushing
 	over HTTPS. Can be overridden by the 'GIT_SSL_NO_VERIFY' environment

http.c

@@ -41,6 +41,7 @@ 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 *curl_cookie_file;
 static char *user_name, *user_pass;
 static const char *user_agent;
 
@@ -191,6 +192,9 @@ 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.cookiefile", var))
+		return git_config_string(&curl_cookie_file, var, value);
+
 	if (!strcmp("http.postbuffer", var)) {
 		http_post_buffer = git_config_int(var, value);
 		if (http_post_buffer < LARGE_PACKET_MAX)
@@ -531,6 +535,7 @@ struct active_request_slot *get_active_slot(void)
 	slot->finished = NULL;
 	slot->callback_data = NULL;
 	slot->callback_func = NULL;
+	curl_easy_setopt(slot->curl, CURLOPT_COOKIEFILE, curl_cookie_file);
 	curl_easy_setopt(slot->curl, CURLOPT_HTTPHEADER, pragma_header);
 	curl_easy_setopt(slot->curl, CURLOPT_ERRORBUFFER, curl_errorstr);
 	curl_easy_setopt(slot->curl, CURLOPT_CUSTOMREQUEST, NULL);