code: public GrpcServerBuilder addService(GrpcService serviceDefinition) {
      ServerServiceDefinition service = serviceDefinition.getServiceDefinition();
      if (SecurityUtils.isAuthenticationEnabled(mConfiguration)
          && serviceDefinition.isAuthenticated()) {
        // Intercept the service with authenticated user injector.
        service = ServerInterceptors.intercept(service,
            new AuthenticatedUserInjector(mAuthenticationServer));
      }
      mNettyServerBuilder = mNettyServerBuilder.addService(service);
      return this;
    }
docs: Add a service to this server.
  
  @param serviceDefinition the service definition of new service
  @return an updated instance of this {@link GrpcServerBuilder}