From 973fdaee2697592e708b26795efc6fd013ca8cda Mon Sep 17 00:00:00 2001
From: Pascal Muller <pascalmuller@gmail.com>
Date: Wed, 23 Jun 2021 21:21:10 +0200
Subject: [PATCH] http: optionally send SSL client certificate

This adds support for a new http.sslAutoClientCert config value.

In cURL 7.77 or later the schannel backend does not automatically send
client certificates from the Windows Certificate Store anymore.

This config value is only used if http.sslBackend is set to "schannel",
and can be used to opt in to the old behavior and force cURL to send
client certificates.

This fixes https://github.com/git-for-windows/git/issues/3292

Signed-off-by: Pascal Muller <pascalmuller@gmail.com>
---
 Documentation/config/http.txt |  5 +++++
 git-curl-compat.h             |  8 ++++++++
 http.c                        | 24 +++++++++++++++++++++---
 3 files changed, 34 insertions(+), 3 deletions(-)

diff --git a/Documentation/config/http.txt b/Documentation/config/http.txt
index 9125d93a75b036..ddda264dbed9b7 100644
--- a/Documentation/config/http.txt
+++ b/Documentation/config/http.txt
@@ -234,6 +234,11 @@ http.schannelUseSSLCAInfo::
 	when the `schannel` backend was configured via `http.sslBackend`,
 	unless `http.schannelUseSSLCAInfo` overrides this behavior.
 
+http.sslAutoClientCert::
+	As of cURL v7.77.0, the Secure Channel backend won't automatically
+	send client certificates from the Windows Certificate Store anymore.
+	To opt in to the old behavior, http.sslAutoClientCert can be set.
+
 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
diff --git a/git-curl-compat.h b/git-curl-compat.h
index 703756ba851d5b..8291755f50454f 100644
--- a/git-curl-compat.h
+++ b/git-curl-compat.h
@@ -45,4 +45,12 @@
 #define GIT_CURL_HAVE_CURLOPT_PROTOCOLS_STR 1
 #endif
 
+/**
+ * CURLSSLOPT_AUTO_CLIENT_CERT was added in 7.77.0, released in May
+ * 2021.
+ */
+#if LIBCURL_VERSION_NUM >= 0x074d00
+#define GIT_CURL_HAVE_CURLSSLOPT_AUTO_CLIENT_CERT
+#endif
+
 #endif
diff --git a/http.c b/http.c
index 0361190a8a80e8..59ea21c3da54a4 100644
--- a/http.c
+++ b/http.c
@@ -155,6 +155,8 @@ static int http_schannel_check_revoke_mode =
  */
 static int http_schannel_use_ssl_cainfo;
 
+static int http_auto_client_cert;
+
 static int always_auth_proactively(void)
 {
 	return http_proactive_auth != PROACTIVE_AUTH_NONE &&
@@ -443,6 +445,11 @@ static int http_options(const char *var, const char *value,
 		return 0;
 	}
 
+	if (!strcmp("http.sslautoclientcert", var)) {
+		http_auto_client_cert = git_config_bool(var, value);
+		return 0;
+	}
+
 	if (!strcmp("http.minsessions", var)) {
 		min_curl_sessions = git_config_int(var, value, ctx->kvi);
 		if (min_curl_sessions > 1)
@@ -1060,9 +1067,20 @@ static CURL *get_curl_handle(void)
 	}
 #endif
 
-	if (http_ssl_backend && !strcmp("schannel", http_ssl_backend) &&
-	    http_schannel_check_revoke_mode) {
-		curl_easy_setopt(result, CURLOPT_SSL_OPTIONS, http_schannel_check_revoke_mode);
+	if (http_ssl_backend && !strcmp("schannel", http_ssl_backend)) {
+		long ssl_options = 0;
+		if (http_schannel_check_revoke_mode) {
+			ssl_options |= http_schannel_check_revoke_mode;
+		}
+
+		if (http_auto_client_cert) {
+#ifdef GIT_CURL_HAVE_CURLSSLOPT_AUTO_CLIENT_CERT
+			ssl_options |= CURLSSLOPT_AUTO_CLIENT_CERT;
+#endif
+		}
+
+		if (ssl_options)
+			curl_easy_setopt(result, CURLOPT_SSL_OPTIONS, ssl_options);
 	}
 
 	if (http_proactive_auth != PROACTIVE_AUTH_NONE)