Sitecore Forms Hidden Field Binding

GatedAssetBindingHandler.cs

public class GatedAssetBindingHandler : IBindingHandler
{
  public IBindingHandlerResult GetBindingValue()
  {
      var mediaID = HttpContext.Current.Request.QueryString["mediaid"];
      if (!string.IsNullOrEmpty(mediaID))
      {
          var mediaItem = Sitecore.Context.Database.GetItem(mediaID);
          if (mediaItem != null && mediaItem.Paths.IsMediaItem)
          {
              var theURL = Sitecore.Resources.Media.MediaManager.GetMediaUrl(mediaItem);
              var mediaUrl = Sitecore.Resources.Media.HashingUtils.ProtectAssetUrl(theURL);
              if (string.IsNullOrEmpty(mediaUrl))
              {
                  return new NoBindingValueFoundResult();
              }

              return new BindingValueFoundResult(mediaUrl);
          }
          else
          {
              return new NoBindingValueFoundResult();
          }
      }
      else
      {
          return new NoBindingValueFoundResult();
      }
  }

  public void StoreBindingValue(object newValue)
  {
      if (newValue is string mediaUrl)
      {
          newValue = mediaUrl;
      }
  }
}

GatedAssetBindingHandlerLoader.cs

public class GatedAssetBindingHandlerLoader : MvcPipelineProcessor<LoadFieldBindingHandlersArgs>
{
    public override void Process(LoadFieldBindingHandlersArgs args)
    {
        var tokenKey = new FieldBindingTokenKey("Gated Asset Binding Handler", "GatedAssetDownloadForm",
            "Gated Asset Binding Handler");
        args.FieldBindingHandlers.Add(tokenKey, new GatedAssetBindingHandler());
    }
}