Setting HttpContext.User to a custom Domain rather that System.Security.Identity.User

Global.asax.cs

void WindowsAuthentication_OnAuthenticate(object sender, WindowsAuthenticationEventArgs e)
{
        // Instantiate a user repository so as to get User information
	IRepository<User> userRepository = new Repository<User>();
	if (e.Identity != null && e.Identity.IsAuthenticated)
	{
		WindowsIdentity wi = e.Identity;
		User user = userRepository.GetBy(u => u.Name == wi.Name).FirstOrDefault();
                user.Identity = wi; 
		HttpContext.Current.User = user;
	}
}