HTTP Basic 验证客户端的原理：
把HTTP头重的ContentType设置为：application/x-www-form-urlencoded
如果HTTP头没有Authorization，那么添加，并把这个设置为“Basic 用户名：密码”字符串组合的Base64编码。
代码片段：
HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(url);
request.Method = "GET";
request.ContentType = "application/x-www-form-urlencoded";
request.Credentials = CredentialCache.DefaultCredentials;
//获得用户名密码的Base64编码
string code= Convert.ToBase64String(Encoding.ASCII.GetBytes(string.Format("{0}:{1}", "username", "password")));
//添加Authorization到HTTP头
request.Headers.Add("Authorization", "Basic " + code);
HttpWebResponse response = (HttpWebResponse)request.GetResponse();
StreamReader reader = new StreamReader(response.GetResponseStream());
string content= reader.ReadToEnd();
request.Method = "GET";
request.ContentType = "application/x-www-form-urlencoded";
request.Credentials = CredentialCache.DefaultCredentials;
//获得用户名密码的Base64编码
string code= Convert.ToBase64String(Encoding.ASCII.GetBytes(string.Format("{0}:{1}", "username", "password")));
//添加Authorization到HTTP头
request.Headers.Add("Authorization", "Basic " + code);
HttpWebResponse response = (HttpWebResponse)request.GetResponse();
StreamReader reader = new StreamReader(response.GetResponseStream());
string content= reader.ReadToEnd();