http.c: add http.sslCertPasswordProtected option

Add a configuration option, http.sslCertPasswordProtected, and associated
environment variable, GIT_SSL_CERT_PASSWORD_PROTECTED, to enable SSL client
certificate password prompt from within git.  If this option is false and
if the environment variable does not exist, git falls back to OpenSSL's
prompts (as in earlier versions of git).

The environment variable may only be used to enable, not to disable
git's password prompt.  This behavior mimics GIT_NO_VERIFY; the mere
existence of the variable is all that is checked.

Signed-off-by: Mark Lodato <lodatom@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config.txt

@@ -1043,6 +1043,12 @@ http.sslKey::
 	over HTTPS. Can be overridden by the 'GIT_SSL_KEY' environment
 	variable.
 
+http.sslCertPasswordProtected::
+	Enable git's password prompt for the SSL certificate.  Otherwise
+	OpenSSL will prompt the user, possibly many times, if the
+	certificate or private key is encrypted.  Can be overridden by the
+	'GIT_SSL_CERT_PASSWORD_PROTECTED' environment variable.
+
 http.sslCAInfo::
 	File containing the certificates to verify the peer with when
 	fetching or pushing over HTTPS. Can be overridden by the

http.c

@@ -140,6 +140,11 @@ static int http_options(const char *var, const char *value, void *cb)
 #endif
 	if (!strcmp("http.sslcainfo", var))
 		return git_config_string(&ssl_cainfo, var, value);
+	if (!strcmp("http.sslcertpasswordprotected", var)) {
+		if (git_config_bool(var, value))
+			ssl_cert_password_required = 1;
+		return 0;
+	}
 #ifdef USE_CURL_MULTI
 	if (!strcmp("http.maxrequests", var)) {
 		max_requests = git_config_int(var, value);
@@ -360,7 +365,9 @@ void http_init(struct remote *remote)
 
 	if (remote && remote->url && remote->url[0]) {
 		http_auth_init(remote->url[0]);
-		if (!prefixcmp(remote->url[0], "https://"))
+		if (!ssl_cert_password_required &&
+		    getenv("GIT_SSL_CERT_PASSWORD_PROTECTED") &&
+		    !prefixcmp(remote->url[0], "https://"))
 			ssl_cert_password_required = 1;
 	}