如何在用户名和密码中再添加一个字段，用于在ASP.NET Identity中创建帐户和进行身份验证？

public class CustomUser : IdentityUser
{
    public string ExtraField { get; set; }
}

services.AddIdentity<CustomUser, IdentityRole>()
        .AddEntityFrameworkStores<ApplicationDbContext>()
        .AddDefaultTokenProviders();

var user = new CustomUser { UserName = "exampleuser", ExtraField = "extra value" };
var result = await _userManager.CreateAsync(user, "password");

var user = await _userManager.FindByNameAsync("exampleuser");
var result = await _signInManager.PasswordSignInAsync(user.UserName, "password", false, lockoutOnFailure: false);
if (result.Succeeded && user.ExtraField == "extra value")
{
    // 身份验证成功，执行相应操作
}