xds: Don't fall back to creds from parent channel, and add insecure creds.

src/core/ext/xds/xds_client.cc

@@ -1780,37 +1780,31 @@ grpc_millis GetRequestTimeout(const grpc_channel_args& args) {
 grpc_channel* CreateXdsChannel(const XdsBootstrap& bootstrap,
                                const grpc_channel_args& args,
                                grpc_error** error) {
-  grpc_channel_credentials* creds = nullptr;
-  RefCountedPtr<grpc_channel_credentials> creds_to_unref;
-  if (!bootstrap.server().channel_creds.empty()) {
-    for (size_t i = 0; i < bootstrap.server().channel_creds.size(); ++i) {
-      if (bootstrap.server().channel_creds[i].type == "google_default") {
-        creds = grpc_google_default_credentials_create(nullptr);
-        break;
-      } else if (bootstrap.server().channel_creds[i].type == "fake") {
-        creds = grpc_fake_transport_security_credentials_create();
-        break;
-      }
-    }
-    if (creds == nullptr) {
-      *error = GRPC_ERROR_CREATE_FROM_STATIC_STRING(
-          "no supported credential types found");
-      return nullptr;
+  RefCountedPtr<grpc_channel_credentials> creds;
+  for (const auto& channel_creds : bootstrap.server().channel_creds) {
+    if (channel_creds.type == "google_default") {
+      creds.reset(grpc_google_default_credentials_create(nullptr));
+      break;
     }
-    creds_to_unref.reset(creds);
-  } else {
-    creds = grpc_channel_credentials_find_in_args(&args);
-    if (creds == nullptr) {
-      // Built with security but parent channel is insecure.
+    if (channel_creds.type == "insecure") {
       return grpc_insecure_channel_create(bootstrap.server().server_uri.c_str(),
                                           &args, nullptr);
     }
+    if (channel_creds.type == "fake") {
+      creds.reset(grpc_fake_transport_security_credentials_create());
+      break;
+    }
+  }
+  if (creds == nullptr) {
+    *error = GRPC_ERROR_CREATE_FROM_STATIC_STRING(
+        "no supported credential types found");
+    return nullptr;
   }
   const char* arg_to_remove = GRPC_ARG_CHANNEL_CREDENTIALS;
   grpc_channel_args* new_args =
       grpc_channel_args_copy_and_remove(&args, &arg_to_remove, 1);
   grpc_channel* channel = grpc_secure_channel_create(
-      creds, bootstrap.server().server_uri.c_str(), new_args, nullptr);
+      creds.get(), bootstrap.server().server_uri.c_str(), new_args, nullptr);
   grpc_channel_args_destroy(new_args);
   return channel;
 }