[PATCH +warn] Implement https public key pinning

[Christoph Egger <christoph@christoph-egger.org>]

Add the http.pinnedpubkey configuration option for public key
pinning. It allows any string supported by libcurl --
base64(sha256(pubkey)) or filename of the full public key.

If cURL does not support pinning (is too old) output a warning to the
user.

Signed-off-by: Christoph Egger <christoph@christoph-egger.org>
---

 This version of the patch adds a warning to the user if the option is
 not supported.

 Documentation/config.txt |  8 ++++++++
 http.c                   | 14 ++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/Documentation/config.txt b/Documentation/config.txt
index 27f02be..0f2643b 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -1727,6 +1727,14 @@ http.sslCAPath::
 	with when fetching or pushing over HTTPS. Can be overridden
 	by the 'GIT_SSL_CAPATH' environment variable.
 
+http.pinnedpubkey::
+	Public key of the https service. It may either be the filename of
+	a PEM or DER encoded public key file or a string starting with
+	'sha256//' followed by the base64 encoded sha256 hash of the
+	public key. See also libcurl 'CURLOPT_PINNEDPUBLICKEY'. git will
+	exit with an error if this option is set but not supported by
+	cURL.
+
 http.sslTry::
 	Attempt to use AUTH SSL/TLS and encrypted data transfers
 	when connecting via regular FTP protocol. This might be needed
diff --git a/http.c b/http.c
index dfc53c1..0bb9237 100644
--- a/http.c
+++ b/http.c
@@ -57,6 +57,9 @@ static const char *ssl_key;
 #if LIBCURL_VERSION_NUM >= 0x070908
 static const char *ssl_capath;
 #endif
+#if LIBCURL_VERSION_NUM >= 0x072c00
+static const char *ssl_pinnedkey;
+#endif
 static const char *ssl_cainfo;
 static long curl_low_speed_limit = -1;
 static long curl_low_speed_time = -1;
@@ -239,6 +242,13 @@ static int http_options(const char *var, const char *value, void *cb)
 	if (!strcmp("http.sslcapath", var))
 		return git_config_pathname(&ssl_capath, var, value);
 #endif
+	if (!strcmp("http.pinnedpubkey", var))
+#if LIBCURL_VERSION_NUM >= 0x072c00
+		return git_config_pathname(&ssl_pinnedkey, var, value);
+#else
+		warning(_("Public key pinning not supported with cURL < 7.44.0"));
+		return 0;
+#endif
 	if (!strcmp("http.sslcainfo", var))
 		return git_config_pathname(&ssl_cainfo, var, value);
 	if (!strcmp("http.sslcertpasswordprotected", var)) {
@@ -499,6 +509,10 @@ static CURL *get_curl_handle(void)
 	if (ssl_capath != NULL)
 		curl_easy_setopt(result, CURLOPT_CAPATH, ssl_capath);
 #endif
+#if LIBCURL_VERSION_NUM >= 0x072c00
+	if (ssl_pinnedkey != NULL)
+		curl_easy_setopt(result, CURLOPT_PINNEDPUBLICKEY, ssl_pinnedkey);
+#endif
 	if (ssl_cainfo != NULL)
 		curl_easy_setopt(result, CURLOPT_CAINFO, ssl_cainfo);
 
-- 
2.7.0


--