Request.Headers.Add("Authorization", "Basic base64(用户名:密码)")

using System;
using System.IO;
using System.Net;
using System.Text;
using System.Xml;

namespace ConsoleApplication1
{
    public static class Domain
    {
        /// <summary>
        /// 域名查询
        /// </summary>
        /// <param name="domain"></param>
        /// <returns>
        ///     1   : free
        ///     -1  : taken
        ///     -2  : error
        /// </returns>
        public static int Check(string domain)
        {
            int result = 0;
            try
            {
                Encoding encoding = Encoding.GetEncoding("utf-8");
                Uri uri = new Uri(string.Format("http://api.domainapi.com/v1/availability/xml/{0}", domain));
                string basic = string.Format("Basic {0}", Convert.ToBase64String(new ASCIIEncoding().GetBytes("dnawo:password12345")));
                WebRequest webRequest = WebRequest.Create(uri);
                webRequest.Headers.Add("Authorization", basic);
                WebResponse webResponse = webRequest.GetResponse();
                using (StreamReader streamReader = new StreamReader(webResponse.GetResponseStream(), encoding))
                {
                    XmlDocument xmlDocument = new XmlDocument();
                    xmlDocument.LoadXml(streamReader.ReadToEnd());
                    XmlNode xmlNode = xmlDocument.SelectSingleNode("/response/content/domainList/domain/status");
                    if (xmlNode != null)
                    {
                        if (xmlNode.InnerText == "free")
                            result = 1;
                        else
                            result = -1;
                    }
                }
            }
            catch
            {
                result = -2;
            }

            return result;
        }
    }
}