How to generate validation attributes for custom tag helper

I am creating a tag helper for a composite, custom dropdown list:

[HtmlTargetElement("mwrdropdown")]
public class MwrDropDownTagHelper : TagHelper
{
     public string AspFor { get; set; }
     public List<SelectListItem> SelectList { get; set; }

     public override void Process(TagHelperContext context, TagHelperOutput output)
     {
         output.TagName = "div";
         output.Attributes["class"] = "mwr-drop-down";

         TagBuilder textArea = new TagBuilder("div");
         textArea.Attributes["class"] = "mwr-drop-down-text";

         TagBuilder textSpan = new TagBuilder("span");
         textSpan.InnerHtml.Append(SelectList[0].Text);
         textSpan.AddCssClass("mwr-drop-down-text-span");

         TagBuilder arrow = new TagBuilder("i");
         arrow.AddCssClass("fa fa-chevron-circle-down mwr-drop-arrow");

         TagBuilder dropPanel = new TagBuilder("div");
         dropPanel.AddCssClass("mwr-drop-panel");

         int counter = 0;

         foreach(var item in SelectList)
         {
             TagBuilder selectItem = new TagBuilder("div");
             selectItem.MergeAttribute("data-select-value", item.Value);
             selectItem.AddCssClass("mwr-select-item");
             if (counter == 0) { selectItem.AddCssClass("selected"); }
             selectItem.InnerHtml.Append(item.Text);
             dropPanel.InnerHtml.Append(selectItem);++counter;
         }

         TagBuilder hidden = new TagBuilder("input");
         hidden.MergeAttribute("type", "hidden");
         hidden.MergeAttribute("asp-for", AspFor);
         textArea.InnerHtml.Append(textSpan);
         textArea.InnerHtml.Append(arrow);
         output.Content.Append(textArea);
         output.Content.Append(dropPanel);
         output.Content.Append(hidden);

     }//Process()

}//class MwrDropDownTagHelper

My View Model class has a Required Annotation for the Category Property

and this is my markup:

<mwrdropdown asp-for="Category" select-list="@Model.Categories"></mwrdropdown>

Here is the generated html:

<div class="mwr-drop-down"><div class="mwr-drop-down-text"><span class="mwr-drop-down-text-span">select a category</span><i class="fa fa-chevron-circle-down mwr-drop-arrow"></i></div><div class="mwr-drop-panel"><div class="selected mwr-select-item" data-select-value="">select a category</div><div class="mwr-select-item" data-select-value="tutorial">tutorial</div><div class="mwr-select-item" data-select-value="article">article</div></div><input asp-for="Category" type="hidden"></div>

I was hoping that I could just "pass through" the  - asp-for -  attribute and  the framework would generate the validation attributes. I am guessing these are generating before my "trans-piled" html hits the DOM. Is there anyway to do this without having to manually populate the validation attributes?

Thanks in advance!