SaveChangesAuditing.cs

public override int SaveChanges()
{
    ModifyBaseEntity();

    return base.SaveChanges();
}

private void ModifyBaseEntity()
{ 

    var objectStateEntries =
        ChangeTracker.Entries().Where(x => ((x.State == EntityState.Added) || (x.State == EntityState.Modified)) && x.Entity is BaseEntity);

    var currentTime = DateTime.UtcNow;

    foreach (var entry in objectStateEntries)
    {
        var entityBase = entry.Entity as IBaseEntity;

        var userId = _httpContextAccessor.HttpContext.User.Identity.Name;

        if (entry.State == EntityState.Added)
        {
            if (entityBase != null)
            {
                entityBase.CreatedDateTime = currentTime;
                entityBase.CreatedByUserId = userId;
            }
        }

        if (entityBase != null)
        {
            entityBase.ModifiedDateTime = currentTime;
            entityBase.ModifiedByUserId = userId;
        }
    }
}