doLogin

- (void)loginWithOnce:(NSString *)once
{
    NSHTTPCookieStorage *storage = [NSHTTPCookieStorage sharedHTTPCookieStorage];
    for (NSHTTPCookie *cookie in [storage cookies]) {
        [storage deleteCookie:cookie];
    }
    
    NSDictionary *parameters = @{
                                 @"once" : once,
                                 @"next" : @"/",
                                 @"p" : self.txtPassword.text,
                                 @"u" : self.txtUsername.text,
                                 };
    
    NSLog(@"PARAMETERS: %@", parameters);
    
    [self.manager.requestSerializer setValue:@"www.v2ex.com" forHTTPHeaderField:@"Host"];
    [self.manager.requestSerializer setValue:@"https://www.v2ex.com" forHTTPHeaderField:@"Origin"];
    [self.manager.requestSerializer setValue:@"https://www.v2ex.com/signin" forHTTPHeaderField:@"Referer"];
    [self.manager.requestSerializer setValue:@"1" forHTTPHeaderField:@"Upgrade-Insecure-Requests"];
    [self.manager.requestSerializer setValue:@"application/x-www-form-urlencoded" forHTTPHeaderField:@"Content-Type"];
    [self.manager.requestSerializer setValue:@"zh-CN,zh;q=0.8,ja;q=0.6,zh-TW;q=0.4" forHTTPHeaderField:@"Accept-Language"];
    [self.manager.requestSerializer setValue:@"Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_2) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/34.0.1847.116 Safari/537.36" forHTTPHeaderField:@"User-Agent"];
    
    [self.manager POST:@"https://www.v2ex.com/signin" parameters:parameters
                                                        success:^void(NSURLSessionDataTask * task, id responseObject) {
                                                            NSString *HTMLString = [[NSString alloc] initWithData:responseObject encoding:NSUTF8StringEncoding];
                                                            NSLog(@"%@", HTMLString);

                                                        }failure:^void(NSURLSessionDataTask * operation, NSError * error) {
                                                       
                                                        }];
    
}