需求：删除 qq 登录的 cookie，保证下次打开 qq 登录页面不会默认登录

实现：

     NSString *url =@"https://w.mail.qq.com/cgi-bin/loginpage?

f=xhtml&kvclick=loginpage|app_push|enter|ios&ad=false&f=xhtml";//qq登录的 url

     NSString *urlString =[url stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];

     NSArray * cookArray = [[NSHTTPCookieStorage sharedHTTPCookieStorage] cookiesForURL:[NSURL URLWithString:urlString]];

     for (NSHTTPCookie *cookie in cookArray)

     {

         if ([cookie.domain containsString:@"qq.com"])

         {

             [[NSHTTPCookieStorage sharedHTTPCookieStorage] deleteCookie:cookie];

         }

     }