Enforce domain name in Asp.Net Core

DomainEnforcer.cs

using System;

namespace Microsoft.AspNet.Builder
{
    public static class DomainEnforcer
    {
        public static IApplicationBuilder UseDomainEnforcer(this IApplicationBuilder app, string domainToEnforce)
        {
            if (string.IsNullOrEmpty(domainToEnforce))
                throw new ArgumentNullException(nameof(domainToEnforce));

            Func<RequestDelegate, RequestDelegate> middleware = next => async context =>
            {
                var req = context.Request;
                var res = context.Response;

                if (req.Host.HasValue && req.Host.Value == domainToEnforce)
                    await next(context);
                else
                    res.Redirect($"{req.Scheme}://{domainToEnforce}{req.Path}{req.QueryString}");
            };

            return app.Use(middleware);
        }
    }
}

Startup.cs

namespace MyProject
{
    public class Startup
    {
        public void Configure(IApplicationBuilder app)
        {
            app.UseDomainEnforcer("example.com");
        }
    }
}