Hello,

I am building a website on Umbraco 8 and I need to add rel="noopener noreferrer" to every anchor that contains external url.

After some time googling on how to do it I figured I can overtake the generated html before the rendering and add the rel attribute where required. (Source)

To manage it I have made a class implementing ActionFilterAttribute interface:

internal class HtmlAnchorUpdateFilter : ActionFilterAttribute
{
    public override void OnActionExecuting(ActionExecutingContext filterContext)
    {
        var stringBuilder = new StringBuilder();
        filterContext.HttpContext.Items["output"] = filterContext.RequestContext.HttpContext.Response.Output;
        filterContext.RequestContext.HttpContext.Response.Output = new HtmlTextWriter(new StringWriter(stringBuilder));
        filterContext.HttpContext.Items["stringBuilder"] = stringBuilder;
    }

    public override void OnResultExecuted(ResultExecutedContext filterContext)
    {
        var response = filterContext.HttpContext.Items["stringBuilder"].ToString();
        var output = filterContext.HttpContext.Items["output"] as StringWriter;
        output?.Write(response);
    }
}

Also, I have registered it in the global filters using IComposer:

public class FilterComposer : IComposer
{
    public void Compose(Composition composition)
    {
        GlobalFilters.Filters.Add(new HtmlAnchorUpdateFilter());
    }
}

Of course this does not work as I expect it. Though the Filter attribute is getting called it gets called twice on a partial view html and not the final complete html.

So my questions are:

1. Is there a better approach to this problem?
2. If not, then how can I overtake the final generated html?