asp.net core mvc의 특정 컨트롤러에 두 번째 수준 도메인 이름을 바인딩하는 방법

app.UseMvc(routes =>
{
      routes.MapRoute(
           name: "default",
           template: "{controller=Home}/{action=Index}/{id?}",
           defaults: new { area="admin"});
});

　　public class SubDomainRouter : RouteBase
    {
        private readonly IRouter _target;
        private readonly string _subDomain;
        public SubDomainRouter(
           IRouter target,
           string subDomain,//当前路由规则绑定的二级域名
           string routeTemplate,
           RouteValueDictionary defaults,
           RouteValueDictionary constrains,
           IInlineConstraintResolver inlineConstraintResolver)
           : base(routeTemplate,
                  subDomain,
                  inlineConstraintResolver,
                  defaults,
                  constrains,
                  new RouteValueDictionary(null))
        {
            if (target == null)
            {
                throw new ArgumentNullException(nameof(target));
            }
            if (subDomain == null)
            {
                throw new ArgumentNullException(nameof(subDomain));
            }
            _subDomain = subDomain;
            _target = target;
        }
        public override Task RouteAsync(RouteContext context)
        {
            string domain = context.HttpContext.Request.Host.Host;//获取当前请求域名，然后跟_subDomain比较，如果不想等，直接忽略
           
            if (string.IsNullOrEmpty(domain) || string.Compare(_subDomain, domain) != 0)
            {
                return Task.CompletedTask;
            }
　　　　　　　　
　　　　　　 //如果域名匹配，再去验证访问路径是否匹配

            return base.RouteAsync(context);
            
        }

        protected override Task OnRouteMatched(RouteContext context)
        {
            context.RouteData.Routers.Add(_target);
            return _target.RouteAsync(context);
        }

        protected override VirtualPathData OnVirtualPathGenerated(VirtualPathContext context)
        {
            return _target.GetVirtualPath(context);
        }
    }

public static class RouteBuilderExtensions
    {
        public static IRouteBuilder MapDomainRoute(
            this IRouteBuilder routeBuilder,string domain,string area,string controller)
        {
            if(string.IsNullOrEmpty(area)||string.IsNullOrEmpty(controller))
            {
                throw new ArgumentNullException("area or controller can not be null");
            }
            var inlineConstraintResolver = routeBuilder
                .ServiceProvider
                .GetRequiredService<IInlineConstraintResolver>();

                string template = "";

                    RouteValueDictionary defaults = new RouteValueDictionary();
                    RouteValueDictionary constrains = new RouteValueDictionary();
                    constrains.Add("area", area);
                    defaults.Add("area", area);
                    constrains.Add("controller", controller);
                    defaults.Add("controller", string.IsNullOrEmpty(controller) ? "home" : controller);
                    defaults.Add("action", "index");
                    
                    template += "{action}/{id?}";//路径规则中不再包含控制器信息，但是上面通过constrains限定了查找时所要求的控制器名称
                    routeBuilder.Routes.Add(new SubDomainRouter(routeBuilder.DefaultHandler, domain, template, defaults, constrains, inlineConstraintResolver));

            
            return routeBuilder;
        }
}

app.UseMvc(
      routes =>
        {
            routes.MapDomainRoute("xxx.domain.com","areaname","controllername");
                        
            routes.MapRoute(
                  name: "default",
                  template: "{controller=Home}/{action=Index}/{id?}",
                  defaults: new { area = "web" });
        });