Merge branch 'ce/https-public-key-pinning'

You can now set http.[<url>.]pinnedpubkey to specify the pinned
public key when building with recent enough versions of libcURL.

* ce/https-public-key-pinning:
  http: implement public key pinning

Documentation/config.txt

@@ -1733,6 +1733,14 @@ 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

http.c

@@ -62,6 +62,9 @@ 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;
@@ -310,6 +313,15 @@ static int http_options(const char *var, const char *value, void *cb)
 		return 0;
 	}
 
+	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
+	}
+
 	/* Fall back on the default ones */
 	return git_default_config(var, value, cb);
 }
@@ -512,6 +524,10 @@ static CURL *get_curl_handle(void)
 #if LIBCURL_VERSION_NUM >= 0x070908
 	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);