mef-owin

[assembly: OwinStartupAttribute(typeof(Foo.Startup))]
namespace Foo
{
    public partial class Startup
    {
        public void Configuration(IAppBuilder app)
        {
            ConfigureAuth(app);
            
            // add filter for your dlls
            ControllerBuilder.Current.SetControllerFactory(new MefControllerFactory(MefConfig.Build("*Foo*Plugin.dll")));
        }
    }

    public static class MefConfig
    {
        public static CompositionContainer Container { get; private set; }

        public static CompositionContainer Build(string filter = "*.dll")
        {
            var files = Directory.GetFiles(AppDomain.CurrentDomain.BaseDirectory, filter, SearchOption.AllDirectories)
                .Where(_ => !_.Replace(AppDomain.CurrentDomain.BaseDirectory, "").Contains(@"obj\"));

            var catalogAggregator = new AggregateCatalog();

            foreach (var file in files)
            {
                catalogAggregator.Catalogs.Add(new AssemblyCatalog(Assembly.LoadFrom(file)));
            }

            Container = new CompositionContainer(catalogAggregator);
            return Container;
        }
    }

    public class MefControllerFactory : DefaultControllerFactory
    {
        private readonly CompositionContainer _container;

        public MefControllerFactory(CompositionContainer container)
        {
            _container = container;
        }

        protected override IController GetControllerInstance(System.Web.Routing.RequestContext requestContext, Type controllerType)
        {
            IController controller = null;

            var export = _container.GetExports(typeof(IController), null, controllerType.FullName).SingleOrDefault();
            if (export != null)
            {
                controller = export.Value as IController;
                if (controller != null)
                {
                    _container.SatisfyImportsOnce(controller);
                }
            }

            return controller;
        }
    }
}