Added function signatures for plugin wrapping

src/node/ext/credentials.h

@@ -69,6 +69,7 @@ class Credentials : public ::node::ObjectWrap {
   static NAN_METHOD(CreateFake);
   static NAN_METHOD(CreateIam);
   static NAN_METHOD(CreateInsecure);
+  static NAN_METHOD(CreateFromPlugin);
   static NanCallback *constructor;
   // Used for typechecking instances of this javascript class
   static v8::Persistent<v8::FunctionTemplate> fun_tpl;
@@ -76,6 +77,19 @@ class Credentials : public ::node::ObjectWrap {
   grpc_credentials *wrapped_credentials;
 };
 
+/* Auth metadata plugin functionality */
+
+typedef struct plugin_state {
+  Nan::Callback *callback;
+} plugin_state;
+
+void plugin_get_metadata(void *state, const char *service_url,
+                         grpc_credentials_plugin_metadata_cb cb, void *user_data);
+
+void plugin_destroy_state(void *state);
+
+static NAN_METHOD(PluginCallback);
+
 }  // namespace node
 }  // namespace grpc