Using controllers from an external assembly in ASP.NET Web API

WebApiConfig.cs

public static class WebApiConfig
    {
        public static void Register(HttpConfiguration config)
        {
            // Web API configuration and services
            // Configure Web API to use only bearer token authentication.
            config.SuppressDefaultHostAuthentication();
            config.Filters.Add(new HostAuthenticationFilter(OAuthDefaults.AuthenticationType));
            config.Services.Replace(typeof(IAssembliesResolver),new DynamicAssemblyResolver());
            // Web API routes
            config.MapHttpAttributeRoutes();

            config.Routes.MapHttpRoute(
                name: "DefaultApi",
                routeTemplate: "api/{controller}/{id}",
                defaults: new { id = RouteParameter.Optional }
            );
        }
    }

    public class DynamicAssemblyResolver
        :IAssembliesResolver
    {
        public ICollection<Assembly> GetAssemblies()
        {
            return AppDomain.CurrentDomain.GetAssemblies();
        }
    }