Microsoft.Extensions.DependencyInjection with OWIN Self-Hosted WebAPI

0 - ServiceHost.cs

// ...
using Microsoft.Owin.Hosting;
// ...

public class ServiceHost
{
  private IDisposable server = null;
  const string baseAddress = "https://*:443";

  public void Start()
  {
    server = WebApp.Start<WebApiStartup>(baseAddress);
  }

1 - WebApiStartup.cs

public class WebApiStartup
{
  public void Configuration(IAppBuilder appBuilder)
  {
    appBuilder.Map("/api", api =>
    {
      var config = new HttpConfiguration();
      config.MapHttpAttributeRoutes();

      // Add IoC
      var serviceProvider = IocStartup.BuildServiceProvider();
      config.DependencyResolver = new DefaultDependencyResolver(serviceProvider);
      
      // ...
      api.UseCors(CorsOptions.AllowAll);
      api.UseWebApi(config);
    });

    // ...

2 - DefaultDependencyResolver.cs

// ...
using System.Web.Http.Dependencies;
using Microsoft.Extensions.DependencyInjection;
// ...

public class DefaultDependencyResolver : IDependencyResolver
{
  private readonly IServiceProvider provider;

  public DefaultDependencyResolver(IServiceProvider provider)
  {
      this.provider = provider;
  }

  public object GetService(Type serviceType)
  {
      return provider.GetService(serviceType);
  }

  public IEnumerable<object> GetServices(Type serviceType)
  {
      return provider.GetServices(serviceType);
  }

  public IDependencyScope BeginScope()
  {
      return this;
  }

  public void Dispose()
  {
  }
}

3 - IocStartup.cs

public static class IocStartup
{
  public static IServiceProvider BuildServiceProvider()
  {
    var services = new ServiceCollection();
    // Register all dependent services
    // 
    // IocSomeAssembly.Register(services);    
    // 
    // services.AddTransient<ISomething, Something>()
    
    // For WebApi controllers, you may want to have a bit of reflection
    var controllerTypes = Assembly.GetExecutingAssembly().GetExportedTypes()
      .Where(t => !t.IsAbstract && !t.IsGenericTypeDefinition)
      .Where(t => typeof(ApiController).IsAssignableFrom(t)
        || t.Name.EndsWith("Controller", StringComparison.OrdinalIgnoreCase));
    foreach (var type in controllerTypes)
    {
      services.AddTransient(type);
    }
    
    // It is only that you need to get service provider in the end
    var serviceProvider = services.BuildServiceProvider();
    return serviceProvider;
  }
}