string username="username";

string password="password";

//注意这里的格式哦，为 "username:password"

string usernamePassword = username + ":" + password;

CredentialCache mycache = new CredentialCache();

mycache.Add(new Uri(url), "Basic", new NetworkCredential(username, password));

myReq.Credentials = mycache;

myReq.Headers.Add("Authorization", "Basic " + Convert.ToBase64String(new ASCIIEncoding().GetBytes(usernamePassword))); 

WebResponse wr = myReq.GetResponse();

Stream receiveStream = wr.GetResponseStream();

StreamReader reader = new StreamReader(receiveStream, Encoding.UTF8);

string content = reader.ReadToEnd();