Set current user as default value in Model in ASP.Net MVC

I am attempting to capture the current logged-in user's identity when they submit a record, but it's not working - the value for the field remains null.  I think it may be due to the fact that I am using Active Directory for authentication, but I'm not sure.  here' the model:

How to set current user as default value for a field in the model in MVC

using System;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;
using System.Web;

namespace phaudmvc.Models
{
    public class Phaud
    {
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public int Id { get; set; }

        [Required, MaxLength(128), Display(Name = "Created By")]
        public string PaCrtdBy { get; set; } = HttpContext.Current.User.Identity.Name;

        [Display(Name = "Date Created"), Required]
        public DateTime PaCrtdDt { get; set; } = DateTime.Now;

        [Required, MaxLength(128), Display(Name = "Manager")]
        public string Mgr { get; set; }

        [Required, MaxLength(128), Display(Name = "Department")]
        public string Dept { get; set; }
}

What do I need to change to get this field value to always default to the current logged-in user?