nghttpx: Add --verify-client-cacert option

Using --cacert to load certificate for client certificate authentication
is problematic since, --cacert is also used for client mode.
This commit adds --verify-client-cacert option which specify the CA
certficate file used only for client certificate validation.
This change also removes the default certficate load function for
client certificate validation.

src/shrpx.cc

@@ -336,7 +336,6 @@ void fill_default_config()
 
   mod_config()->verbose = false;
   mod_config()->daemon = false;
-  mod_config()->verify_client = false;
 
   mod_config()->server_name = "nghttpx nghttp2/" NGHTTP2_VERSION;
   set_config_str(&mod_config()->host, "0.0.0.0");
@@ -418,6 +417,7 @@ void fill_default_config()
   mod_config()->write_burst = 0;
   mod_config()->npn_list = nullptr;
   mod_config()->verify_client = false;
+  mod_config()->verify_client_cacert = nullptr;
 }
 } // namespace
 
@@ -595,6 +595,11 @@ void print_help(std::ostream& out)
       << "                       as a part of protocol string.\n"
       << "                       Default: " << DEFAULT_NPN_LIST << "\n"
       << "    --verify-client    Require and verify client certificate.\n"
+      << "    --verify-client-cacert=<PATH>\n"
+      << "                       Path to file that contains CA certificates\n"
+      << "                       to verify client certificate.\n"
+      << "                       The file must be in PEM format. It can\n"
+      << "                       contain multiple certificates.\n"
       << "\n"
       << "  HTTP/2.0 and SPDY:\n"
       << "    -c, --spdy-max-concurrent-streams=<NUM>\n"
@@ -733,6 +738,7 @@ int main(int argc, char **argv)
       {"write-burst", required_argument, &flag, 37},
       {"npn-list", required_argument, &flag, 38},
       {"verify-client", no_argument, &flag, 39},
+      {"verify-client-cacert", required_argument, &flag, 40},
       {nullptr, 0, nullptr, 0 }
     };
     int option_index = 0;
@@ -940,6 +946,11 @@ int main(int argc, char **argv)
         // --verify-client
         cmdcfgs.push_back(std::make_pair(SHRPX_OPT_VERIFY_CLIENT, "yes"));
         break;
+      case 40:
+        // --verify-client-cacert
+        cmdcfgs.push_back(std::make_pair(SHRPX_OPT_VERIFY_CLIENT_CACERT,
+                                         optarg));
+        break;
       default:
         break;
       }

src/shrpx_config.cc

@@ -101,6 +101,7 @@ const char SHRPX_OPT_WRITE_RATE[] = "write-rate";
 const char SHRPX_OPT_WRITE_BURST[] = "write-burst";
 const char SHRPX_OPT_NPN_LIST[] = "npn-list";
 const char SHRPX_OPT_VERIFY_CLIENT[] = "verify-client";
+const char SHRPX_OPT_VERIFY_CLIENT_CACERT[] = "verify-client-cacert";
 
 namespace {
 Config *config = nullptr;
@@ -409,6 +410,8 @@ int parse_config(const char *opt, const char *optarg)
     parse_config_npn_list(optarg);
   } else if(util::strieq(opt, SHRPX_OPT_VERIFY_CLIENT)) {
     mod_config()->verify_client = util::strieq(optarg, "yes");
+  } else if(util::strieq(opt, SHRPX_OPT_VERIFY_CLIENT_CACERT)) {
+    set_config_str(&mod_config()->verify_client_cacert, optarg);
   } else if(util::strieq(opt, "conf")) {
     LOG(WARNING) << "conf is ignored";
   } else {

src/shrpx_config.h

@@ -92,6 +92,7 @@ extern const char SHRPX_OPT_WRITE_RATE[];
 extern const char SHRPX_OPT_WRITE_BURST[];
 extern const char SHRPX_OPT_NPN_LIST[];
 extern const char SHRPX_OPT_VERIFY_CLIENT[];
+extern const char SHRPX_OPT_VERIFY_CLIENT_CACERT[];
 
 union sockaddr_union {
   sockaddr sa;
@@ -187,6 +188,9 @@ struct Config {
   size_t npn_list_len;
   // The list of (private key file, certificate file) pair
   std::vector<std::pair<std::string, std::string>> subcerts;
+  // Path to file containing CA certificate solely used for client
+  // certificate validation
+  char *verify_client_cacert;
 };
 
 const Config* get_config();

src/shrpx_ssl.cc

@@ -218,15 +218,12 @@ SSL_CTX* create_ssl_context(const char *private_key_file,
     DIE();
   }
   if(get_config()->verify_client) {
-    if(SSL_CTX_set_default_verify_paths(ssl_ctx) != 1) {
-      LOG(WARNING) << "Could not load system trusted ca certificates: "
-                   << ERR_error_string(ERR_get_error(), nullptr);
-    }
-    if(get_config()->cacert) {
-      if(SSL_CTX_load_verify_locations(ssl_ctx, get_config()->cacert, nullptr)
-         != 1) {
+    if(get_config()->verify_client_cacert) {
+      if(SSL_CTX_load_verify_locations(ssl_ctx,
+                                       get_config()->verify_client_cacert,
+                                       nullptr) != 1) {
         LOG(FATAL) << "Could not load trusted ca certificates from "
-                   << get_config()->cacert << ": "
+                   << get_config()->verify_client_cacert << ": "
                    << ERR_error_string(ERR_get_error(), nullptr);
         DIE();
       }