Cloudflare http handler in C# allows scraping cloudflare protected websites

CloudflareHttpHandler.cs

using System;
using System.Net.Http;
using System.Threading.Tasks;
using System.Text.RegularExpressions;
using System.Threading;
using System.Collections.Generic;
using System.Linq;

using Microsoft.ClearScript.V8;

using HtmlAgilityPack;

/// <summary>
/// A custom Http handler for Cloudflare protected servers
/// </summary>
public class CloudflareHttpHandler : HttpClientHandler
{
	protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
	{
		var task = base.SendAsync(request, cancellationToken);
		
		var response = task.Result;

		if(base.CookieContainer.GetCookieHeader(request.RequestUri).Contains("cf_clearance"))
			return task;
			
		IEnumerable<string> values;
		
		if(response.Headers.TryGetValues("refresh", out values) && values.FirstOrDefault().Contains("URL=/cdn-cgi/") && response.Headers.Server.ToString() == "cloudflare-nginx" )
		{
			Console.WriteLine("Solving cloudflare challenge . . . ");
				
			string content = response.Content.ReadAsStringAsync().Result;
			
			var htmlDocument = new HtmlDocument();
			htmlDocument.LoadHtml(content);
			
			var jschl_vc = htmlDocument.DocumentNode.SelectSingleNode(@".//input[@name=""jschl_vc""]").Attributes["value"].Value;
			var pass = htmlDocument.DocumentNode.SelectSingleNode(@".//input[@name=""pass""]").Attributes["value"].Value;
			
			var script = htmlDocument.DocumentNode.SelectSingleNode(@".//script").InnerText;

			var regex = new string[3] {
				@"setTimeout\(function\(\){(.+)},\s*\d*\s*\)\s*;",
				@"^\n*\s*(var\s+.*?;)",
				@"(?<=\s+;)(.+t.length;)"
			};
			
			string function, vars, calc;
			
			function = Regex.Match(script, regex[0], RegexOptions.Singleline).Value;
			vars = Regex.Match(function, regex[1], RegexOptions.Multiline).Value;
			calc = Regex.Match(function, regex[2], RegexOptions.Singleline).Value
				.Replace("a.value", "var result")
            	.Replace("t.length", (request.RequestUri.Host.Length).ToString());;

            object result;
            using(var engine = new V8ScriptEngine())
            	result = engine.Evaluate("function getAnswer() {" + vars + calc + "return result;" + "} getAnswer();");
                
            Thread.Sleep(5000);
            
            var requestUri = request.RequestUri;
            
            request.RequestUri = new Uri(requestUri, String.Format("cdn-cgi/l/chk_jschl?jschl_vc={0}&pass={1}&jschl_answer={2}", jschl_vc, pass, result.ToString()));
            
            base.SendAsync(request, cancellationToken).Wait();
            
            request.RequestUri = requestUri;
            
            return base.SendAsync(request, cancellationToken);
		}
			
		return task;
	}
}