public virtual int AccessFailedCount { get; set; }

public virtual ICollection<TClaim> Claims { get; }

public virtual string Email { get; set; }

public virtual bool EmailConfirmed { get; set; }

public virtual TKey Id { get; set; }

public virtual bool LockoutEnabled { get; set; }

public virtual DateTime? LockoutEndDateUtc { get; set; }

public virtual ICollection<TLogin> Logins { get; }

public virtual string PasswordHash { get; set; }

public virtual string PhoneNumber { get; set; }

public virtual bool PhoneNumberConfirmed { get; set; }

public virtual ICollection<TRole> Roles { get; }

public virtual string SecurityStamp { get; set; }

public virtual bool TwoFactorEnabled { get; set; }

public virtual string UserName { get; set; }

public class ApplicationUser : IdentityUser
{
    public bool Has_accepted_policy { get; set; }
    public int user_type_id { get; set; }
}

public class ApplicationDbContext : IdentityDbContext<ApplicationUser>
{
    public ApplicationDbContext()
        : base("DefaultConnection")
    {

    }
}

public string Id { get; set; }

[Required]
[StringLength(256)]
public string UserName { get; set; }

public string PasswordHash { get; set; }

public string SecurityStamp { get; set; }

[StringLength(256)]
public string Email { get; set; }

public bool EmailConfirmed { get; set; }

public bool Is_Active { get; set; }

[Required]
[StringLength(128)]
public string Discriminator { get; set; }

public int? user_type_id { get; set; }

public bool Has_accepted_policy { get; set; }

public string PhoneNumber { get; set; }

public bool PhoneNumberConfirmed { get; set; }

public bool TwoFactorEnabled { get; set; }

public DateTime? LockoutEndDateUtc { get; set; }

public bool LockoutEnabled { get; set; }

public int AccessFailedCount { get; set; }

... other virtual properties

IdentityResult result = await UserManager.CreateAsync(user, model.Password);

UserManagerFactory = () => new UserManager<ApplicationUser>(new UserStore<ApplicationUser>());

public AccountController()
    : this(Startup.UserManagerFactory(), Startup.OAuthOptions.AccessTokenFormat)
{
}

public AccountController(UserManager<ApplicationUser> userManager,
    ISecureDataFormat<AuthenticationTicket> accessTokenFormat)
{
    UserManager = userManager;
    AccessTokenFormat = accessTokenFormat;
}

public UserManager<ApplicationUser> UserManager { get; private set; }

UserManagerFactory = () => new UserManager<ApplicationUser>(new UserStore<ApplicationUser>(new ApplicationDbContext()));

UserManagerFactory = () => new UserManager<ApplicationUser>(new UserStore<ApplicationUser>());

UserManagerFactory = () => new UserManager<ApplicationUser>(new UserStore<ApplicationUser>(new ApplicationDbContext()));

<add name="MyConnString" connectionString="Data Source=server; Initial Catalog=db_name; User ID=user_id; Password=password; Connect Timeout=60;" providerName="System.Data.SqlClient" />

public class ApplicationDbContext : IdentityDbContext<ApplicationUser>
{
    public ApplicationDbContext()
        : base("MyConnString")
    {
    }
}

public class ApplicationUserManager : UserManager<ApplicationUser> // the name conflict
{
    public ApplicationUserManager(IUserStore<ApplicationUser> store)
        : base(store)
    {
    }

<add name="DefaultConnection" connectionString="Server=qadb.myserver.com;Database=mydb;User Id=myuser;Password=mypass;" providerName="System.Data.SqlClient" />

public partial class GoldfishDbContext : IdentityDbContext<ApplicationUser>
{
 ....
}

builder.RegisterType<ApplicationUserManager>().InstancePerRequest();

public ApplicationUserManager UserManager
    {
        get
        {
            return _userManager ?? HttpContext.GetOwinContext().GetUserManager<ApplicationUserManager>();
        }
        private set
        {
            _userManager = value;
        }
    }