var app = new WebApp();

app.Map("/sub", builder =>
{
    builder.UseAuth();
});


class WebApp : IAppBuilder, IRouteBuilder
{
    public void UseAuth()
    {
        
    }
}

public interface IAppBuilder
{
    void UseAuth();
}

public interface IRouteBuilder
{

}

static class AppBuilderExtensions
{
    public static IAppBuilder Map(this IAppBuilder app, PathSring path, Action<IAppBuilder> callback) => app;
}

public static class RouteBuilderExtensions
{
    public static IRouteBuilder Map(this IRouteBuilder routes, string path, Delegate callback) => routes;
}

struct PathSring
{
    public PathSring(string? path)
    {
        Path = path;
    }

    public string? Path { get; }

    public static implicit operator PathSring(string? s) => new PathSring(s);

    public static implicit operator string?(PathSring path) => path.Path;
}