Check out example codes for "No IUserTwoFactorTokenProvider<TUser> named 'Default' is registered.'". It will help you in understanding the concepts better.

Code Example 1

// startup.cs
public void ConfigureServices(IServiceCollection services)
{
  // ....
  services.AddIdentityCore<User, UserRole>()
    .AddEntityFrameworkStores<ApplicationDbContext>()
    .AddDefaultTokenProviders(); // Remember to add this line!
  // ....
}

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