Change route to username after registration

Question

I have followed the correct answer marked for this thread How to change route to username after logged in? and my requirement is exactly what the question says. However when I register a new user (I am using username instead of email) the redirection doesn't follow my custom route.

For instance, when I register with username = Janet, the URL looks like localhost/?username=Janet and throws an error. But if I manually remove the "/?username=" and keep localhost/Janet then it shows the landing page of my application.

I have tried to play with return RedirectToAction("Index","Home"); of my register post method but no luck.

Can someone help in this and tell me what am I doing wrong?

Route config

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

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


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

Username constraint

    public class OwinUsernameConstraint : IRouteConstraint
    {
        private object synclock = new object();

        public bool Match(HttpContextBase httpContext, Route route, string parameterName, RouteValueDictionary values, RouteDirection routeDirection)
        {
            if (parameterName == null)
                throw new ArgumentNullException("parameterName");
            if (values == null)
                throw new ArgumentNullException("values");

            object value;
            if (values.TryGetValue(parameterName, out value) && value != null)
            {
                string valueString = Convert.ToString(value, CultureInfo.InvariantCulture);
                return this.GetUsernameList(httpContext).Contains(valueString);
            }
            return false;
        }

        private IEnumerable<string> GetUsernameList(HttpContextBase httpContext)
        {
            string key = "UsernameConstraint.GetUsernameList";
            var usernames = httpContext.Cache[key];
            if (usernames == null)
            {
                lock (synclock)
                {
                    usernames = httpContext.Cache[key];
                    if (usernames == null)
                    {
                        // Retrieve the list of usernames from the database
                        using (var db = ApplicationDbContext.Create())
                        {
                            usernames = (from users in db.Users
                                            select users.UserName).ToList();
                        }

                        httpContext.Cache.Insert(
                            key: key,
                            value: usernames,
                            dependencies: null,
                            absoluteExpiration: Cache.NoAbsoluteExpiration,
                            slidingExpiration: TimeSpan.FromSeconds(15),
                            priority: CacheItemPriority.NotRemovable,
                            onRemoveCallback: null);
                    }
                }
            }

            return (IEnumerable<string>)usernames;
        }
    }

Register controller

        public async Task<ActionResult> Register(RegisterViewModel model)
        {
            if (ModelState.IsValid)
            {
                var user = new ApplicationUser { UserName = model.UserName, Email = model.Email };
                var result = await UserManager.CreateAsync(user, model.Password);
                if (result.Succeeded)
                {
                    await SignInManager.SignInAsync(user, isPersistent:false, rememberBrowser:false);

                    // For more information on how to enable account confirmation and password reset please visit http://go.microsoft.com/fwlink/?LinkID=320771
                    // Send an email with this link
                    // string code = await UserManager.GenerateEmailConfirmationTokenAsync(user.Id);
                    // var callbackUrl = Url.Action("ConfirmEmail", "Account", new { userId = user.Id, code = code }, protocol: Request.Url.Scheme);
                    // await UserManager.SendEmailAsync(user.Id, "Confirm your account", "Please confirm your account by clicking <a href=\"" + callbackUrl + "\">here</a>");

                    return RedirectToAction("Index","Home");
                }
                AddErrors(result);
            }

            // If we got this far, something failed, redisplay form
            return View(model);
        }

Thanks