Multi-step form controller code idea

gistfile1.cs

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.IO;
using System.Linq;
using System.Web.Mvc;
using Newtonsoft.Json;

namespace Web.Controllers
{
    public class RegistrationController : Controller
    {
        private const string SerialisedValuesKey = "SerialisedValues";
        private const string ValidationHashKey = "ValidationHash";
        private const string SecretSalt = "drthSRT$%^7#fgh;awGSEER";

        private static readonly LinkedList<RegistrationFormSteps> FormSteps = new LinkedList<RegistrationFormSteps>(Enums.Enumerate<RegistrationFormSteps>());

        // This isn't used below, but it contains some logic around what might be done for the hidden field tracking.
        private TReturn SaveFormStateAndReturn<TReturn>(Action<RegistrationFormViewModel> modifier, Func<RegistrationFormViewModel, TReturn> returnAccessor)
        {
            var vm = new RegistrationFormViewModel();

            var serialised = Request.Params[SerialisedValuesKey];
            if (!string.IsNullOrEmpty(serialised))
            {
                var expectedHash = (serialised + SecretSalt).ToSha1Hash();
                var hash = Request.Params[ValidationHashKey];
                if (hash != expectedHash)
                    throw new InvalidDataException("User tampered with registration submission");
                vm = JsonConvert.DeserializeObject<RegistrationFormViewModel>(serialised);
            }

            modifier(vm);

            ViewData[SerialisedValuesKey] = JsonConvert.SerializeObject(vm);
            ViewData[ValidationHashKey] = (ViewData[SerialisedValuesKey] + SecretSalt).ToSha1Hash();

            return returnAccessor(vm);
        }

        public ActionResult Step1()
        {
            return View();
        }

        [HttpPost]
        public ActionResult Step1(Step1ViewModel vm)
        {
            return FormStep(RegistrationFormSteps.Step1);
        }

        [HttpPost]
        public ActionResult Step2(Step2ViewModel vm)
        {
            return FormStep(RegistrationFormSteps.Step2);
        }

        private ActionResult FormStep(RegistrationFormSteps currentStep)
        {
            if (!ModelState.IsValid)
                return View(currentStep.ToString(), GetViewModel(currentStep));

            SaveFormState(currentStep);

            var stepToShow = default(RegistrationFormSteps?);
            if (currentStep != FormSteps.First() && Request.Params["previous"] != null)
                stepToShow = GetPreviousStep(currentStep);
            if (currentStep != FormSteps.Last() && (Request.Params["next"] != null))
                stepToShow = GetNextStep(currentStep);

            if (!stepToShow.HasValue && currentStep == FormSteps.Last())
                return ProcessRegistration();

            return View(stepToShow.ToString(), GetViewModel(stepToShow));
        }
    }

    public enum RegistrationFormSteps
    {
        Step1,
        Step2
    }

    public class RegistrationFormViewModel
    {
        public Step1ViewModel Step1 { get; set; }
        public Step2ViewModel Step2 { get; set; }
    }

    public class Step1ViewModel
    {
        [Required]
        public string FirstName { get; set; }

        [Required]
        public string LastName { get; set; }
    }

    public class Step2ViewModel
    {
        [Required]
        public string EmailAddress { get; set; }

        [Required]
        public string Address { get; set; }
    }
}