How to use Swagger as Welcome Page of IAppBuilder in WebAPI

In ASP.NET Core, you can simply just change the RoutePrefix when registering SwaggerUI to empty string.

app.UseSwaggerUI(c =>
{
    c.RoutePrefix = "";
    ...
};

No redirect configuration required, unless you still want /swagger or something similar in the path.

I got this working how I wanted by adding a route in RouteConfig.cs like so:

    public static void RegisterRoutes(RouteCollection routes)
    {
        routes.IgnoreRoute("{resource}.axd/{*pathInfo}");

        routes.MapHttpRoute(
            name: "swagger_root", 
            routeTemplate: "", 
            defaults: null, 
            constraints: null,
            handler: new RedirectHandler((message => message.RequestUri.ToString()), "swagger"));

        routes.MapRoute(
            name: "Default",
            url: "{controller}/{action}/{id}",
            defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }
        );
    }

See this code from swashbuckle to see what's going on: https://github.com/domaindrivendev/Swashbuckle/blob/master/Swashbuckle.Core/Application/RedirectHandler.cs

For Asp.Net core use this:

app.Run(context => {
            context.Response.Redirect("swagger/ui");
            return Task.CompletedTask;
        });

In the Startup.cs file in the Configuration(IAppBuilder app) method I used this line of code to cause it to redirect on load to the swagger welcome page.

app.Run(async context => { 
    context.Response.Redirect("swagger/ui/index"); 
}); 

So the full method I am using is as follows

[assembly: OwinStartup(typeof(AtlasAuthorizationServer.Startup))]
namespace AtlasAuthorizationServer
{
    public partial class Startup
    {
        public void Configuration(IAppBuilder app)
        {
            ConfigureAuth(app);

            HttpConfiguration config = new HttpConfiguration();
            WebApiConfig.Register(config);
            app.UseWebApi(config);

            app.Run(async context => {
                context.Response.Redirect("swagger/ui/index");
            });
        }
    }
}

Note that this is going to cause a green warning in visual studio. I am sure there is some way to mimic this as asynchronous with an await call in the function.