protected void Application_Start()
{
  var builder = new ContainerBuilder();
  // Get your HttpConfiguration.
  var config = GlobalConfiguration.Configuration;
  // Register your Web API controllers.
  builder.RegisterApiControllers(Assembly.GetExecutingAssembly());
  // OPTIONAL: Register the Autofac filter provider.
  builder.RegisterWebApiFilterProvider(config);
  // OPTIONAL: Register the Autofac model binder provider.
  builder.RegisterWebApiModelBinderProvider();
  // Set the dependency resolver to be Autofac.
  var container = builder.Build();
  config.DependencyResolver = new AutofacWebApiDependencyResolver(container);
}