ApplicationDbContext.cs

private void ProcessSave()
{
    var currentTime = DateTimeOffset.UtcNow;
    foreach (var item in ChangeTracker.Entries()
        .Where(e => e.State == EntityState.Added && e.Entity is Entity))
    {
        var entidad = item.Entity as Entity;
        entidad.CreatedDate = currentTime;
        entidad.CreatedByUser = "";
        entidad.ModifiedDate = currentTime;
        entidad.ModifiedByUser = "";
    }

    foreach (var item in ChangeTracker.Entries()
        .Where(predicate: e => e.State == EntityState.Modified && e.Entity is Entity))
    {
        var entidad = item.Entity as Entity;
        entidad.ModifiedDate = currentTime;
        entidad.ModifiedByUser = "";
        item.Property(nameof(entidad.CreatedDate)).IsModified = false;
        item.Property(nameof(entidad.CreatedByUser)).IsModified = false;
    }
}