How to insert a value in Database when using MVC identity framework in AspNetUsers Table?

I want to insert a value in DB and I am using the Asp.Net Identity framework, in my Register method when a new user registers I also want to add a new Id which is client_id by default this id is not inserted by the identity framework?

if (User.IsInRole("Avanceon")) 
{
    var MaxCustomerId = db.AspNetUsers.Max(x => x.Customer_Id);
    if (ModelState.IsValid)
    {   
        var user = new ApplicationUser { UserName = model.UserName, Email = model.Email };
        var result = await UserManager.CreateAsync(user, model.Password);
        if (result.Succeeded)
        {
            // Assign Role to user Here 
            await this.UserManager.AddToRoleAsync(user.Id, model.RoleName);

            // Ends Here
            // await SignInManager.SignInAsync(user, isPersistent: false, rememberBrowser: false);
            ViewBag.userCreated = user.UserName + " Created Successfully";
            ViewBag.Name = new SelectList(context.Roles.ToList(), "Name", "Name");
            MaxCustomerId = MaxCustomerId + 1;
            // db.AspNetUsers.LastOrDefault().Customer_Id = MaxCustomerId;
            db.SaveChanges();
            return View();
            //return RedirectToAction("Index", "Home");
        }

        AddErrors(result);
    }
}

ViewBag.Name = new SelectList(context.Roles.ToList(), "Name", "Name");
return View(model);

You normally can't simply insert any data to AspNetUsers table. You'll need create a class and inherit it from IdentityUser and do the necessary changes in your class.

With code first you should create a class say ApplicationUser which inherits IdentityUser. And add the property there:

public class ApplicationUser : IdentityUser
{
    [Required]
    public string ClientID { get; set; }
}

And then target ApplicationUser (instead of IdentityUser) in your code:

var user = new ApplicationUser
{
    UserName = model.UserName,
    Email = model.Email,
    ClientID = model.ClientID,
};

Make below changes as well:

In ConfigureServices method of Startup.cs

services.AddIdentity<ApplicationUser, IdentityRole>();

In AccountController,

private readonly UserManager<ApplicationUser> _userManager;
private readonly SignInManager<ApplicationUser> _signInManager;

Add migration for this change to take effect