we can use IStartupFilter to Configure http pipline for modules design

[1257960069]

[assembly: HostingStartup(typeof(AppHost))]
public class AppHost : AppHostBase, IHostingStartup
{
    public void Configure(IWebHostBuilder builder) => builder
        .ConfigureServices(services => {
            // Configure ASP.NET Core IOC Dependencies
            services.AddTransient<IStartupFilter,AppHostsStartupFilter>();
        });
//Warn: this Configure method will replace program.cs  var app = builder.Build(); app.UseXXX()
//We should  use  "services.AddTransient<IStartupFilter,AppHostsStartupFilter>();"  this will auto Configure http pipline at first
 .Configure(app =>
 {

 })


    public AppHost() : base("DatagptApi", typeof(MyServices).Assembly) {}

    public override void Configure(Container container)
    {
        // Configure ServiceStack only IOC, Config & Plugins
    }

    public class AppHostsStartupFilter : IStartupFilter
    {
        public Action<IApplicationBuilder> Configure(Action<IApplicationBuilder> next)
        {
            return app =>
            {
                app.UseServiceStack(new AppHost());
                next(app);
            };
        }
    }
}

[mythz]

Thanks for highlighting this, I didn't know there was a way to customize the Web Application which is what was needed to move OpenAPI v3 configuration to Configure.OpenApi.cs which I've just applied to all our Identity Auth .NET 8 templates.

public class ConfigureOpenApi : IHostingStartup
{
    public void Configure(IWebHostBuilder builder) => builder
        .ConfigureServices((context, services) =>
        {
            if (context.HostingEnvironment.IsDevelopment())
            {
                services.AddEndpointsApiExplorer();
                services.AddSwaggerGen();

                services.AddServiceStackSwagger();
                services.AddBasicAuth<Data.ApplicationUser>();
                //services.AddJwtAuth();

                services.AddTransient<IStartupFilter, StartupFilter>();
            }
        });

    public class StartupFilter : IStartupFilter
    {
        public Action<IApplicationBuilder> Configure(Action<IApplicationBuilder> next) => app =>
        {
            app.UseSwagger();
            app.UseSwaggerUI();
            next(app);
        };
    }
}

I've also added an example of this to Modular Startup Docs.