How to save new record with hashed password in my custom table instead of aspnet user?

I am using asp.net identity to create new user but getting error:

Cannot insert the value NULL into column 'Id', table 'Mydb.dbo.AspNetUsers'; column does not allow nulls. INSERT fails.\r\nThe statement has been terminated

But here I don't have any such table like AspNetUsers but instead I have my own table that is Users.

Code: Web.config: 2 conection strings

 <add name="myEntities" connectionString="metadata=res://*/DataModel.csdl|res://*/DataModel.ssdl|res://*/DataModel.msl;provider=System.Data.SqlClient;provider connection string=&quot;data source=;initial catalog=mydb;user id=sa;password=sdfsdfsdf;MultipleActiveResultSets=True;App=EntityFramework&quot;" providerName="System.Data.EntityClient" />
 <add name="MyConnString" connectionString="data source=;initial catalog=Mydb;user id=sa;password=sdfsdfsdf;" providerName="System.Data.SqlClient" />

IdentityModel.cs:

public class ApplicationUser : IdentityUser
    {
        public async Task<ClaimsIdentity> GenerateUserIdentityAsync(UserManager<ApplicationUser> manager)
        {
            // Note the authenticationType must match the one defined in CookieAuthenticationOptions.AuthenticationType
            this.SecurityStamp = Guid.NewGuid().ToString();
            var userIdentity = await manager.CreateIdentityAsync(this, DefaultAuthenticationTypes.ApplicationCookie);
            // Add custom user claims here
            return userIdentity;
        }

        public string Id { get; set; }
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public virtual string Email { get; set; }
        public string Password { get; set; }
        public string Role { get; set; }
        public Nullable<bool> IsActive { get; set; }
        public Nullable<int> CreatedBy { get; set; }
        public Nullable<System.DateTime> CreatedDate { get; set; }
        public Nullable<System.DateTime> LastLogin { get; set; }

        public ApplicationUser()
        {

        }

        public ApplicationUser(string email, string firstName, string lastName, string designation, bool isActive)
        {
            Email = email;
            FirstName = firstName;
            LastName = lastName;
            Designation = designation;
            IsActive = isActive;
        }
    }
  public class ApplicationDbContext : IdentityDbContext<ApplicationUser>
    {
        public ApplicationDbContext()
            : base("MyConnString", throwIfV1Schema: false)
        {
        }

        public static ApplicationDbContext Create()
        {
            return new ApplicationDbContext();
        }
    }

UserStore1.cs:

public class UserStore1 : IUserStore<ApplicationUser>, IUserPasswordStore<ApplicationUser>
    {
        private readonly HttpContext _httpContext;
        UserStore<IdentityUser> userStore = new UserStore<IdentityUser>(new ApplicationDbContext());

        public System.Threading.Tasks.Task CreateAsync(ApplicationUser user)
        {
            HttpContext.Current = _httpContext ?? HttpContext.Current;
            var context = userStore.Context as ApplicationDbContext;
           context.Users.Add(user);
           context.Configuration.ValidateOnSaveEnabled = false;
           context.SaveChanges();
            return Task.FromResult(true);
        }
     }

Controller:

     [Authorize]
    public class AccountController : Controller
    {
        public AccountController()
            : this(new UserManager<ApplicationUser>(new UserStore1()))
        {
        }

        public AccountController(UserManager<ApplicationUser> userManager)
        {
            UserManager = userManager;
        }
        public UserManager<ApplicationUser> UserManager { get; private set; }
[HttpPost]
        [AllowAnonymous]
        [ValidateAntiForgeryToken]
        public async Task<ActionResult> Login(string email, string password, bool rememberMe = false, string returnUrl = null)
        {
            if (ModelState.IsValid)
            {
                var user = new ApplicationUser
                {
                    FirstName= "Abc",
                    LastName= "Pqr",
                    UserName="[email protected]",
                    SecurityStamp = Guid.NewGuid().ToString()
                };

                var result= await UserManager.CreateAsync(user,"123456");
            }
            return View();
        }
    }

Note: I have autogenerated Id in my database table field and that Id is Int.

Update: I am using database first(edmx) and the table that I am using are custom tables for inserting new records(for eg:Users).

At first I have implemented microsoft asp.net identity as shown in below question but 1 user pointed out that I am not using ApplicationUser class which is responsible for handling sign in,cookies etc so I am now trying to use ApplicationUser class:

How to give custom implementation of UpdateAsync method of asp.net identity?

I am really now regretting over my decision to choose Microsoft Identity Framework for Authentication purpose as because I am really finding it complex but now as I have move forward I have to go with it.