import "ViewController.h"

@interface ViewController ()<NSURLSessionTaskDelegate>
@property (nonatomic, strong) NSURLSession *session;
@end

@implementation ViewController

• (NSURLSession *)session {
  if (!_session) {
  NSURLSessionConfiguration *config = [NSURLSessionConfiguration defaultSessionConfiguration];
  _session = [NSURLSession sessionWithConfiguration:config delegate:self delegateQueue:nil];
  }
  return _session;
  }

• (void)viewDidLoad {
  [super viewDidLoad];
  // Do any additional setup after loading the view, typically from a nib.
  }

• (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {

  NSURL *url = [NSURL URLWithString:@"https://kyfw.12306.cn/otn/"];
  [[self.session dataTaskWithURL:url completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {

    NSString *html = [[NSString alloc]initWithData:data encoding:NSUTF8StringEncoding];
    NSLog(@"返回的字符串===%@",html);
  

  }] resume];
  }

pragma mark ---NSURLSessionTaskDelegate代理---

• (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task
  didReceiveChallenge:(NSURLAuthenticationChallenge *)challenge
  completionHandler:(void (^)(NSURLSessionAuthChallengeDisposition disposition, NSURLCredential * _Nullable credential))completionHandler{

  // https工作原理
  // 1.判断身份验证方式是否是服务器验证方法
  if (challenge.protectionSpace.authenticationMethod == NSURLAuthenticationMethodServerTrust) {
  // 2.获取服务器证书
  NSURLCredential *credential = [NSURLCredential credentialForTrust:challenge.protectionSpace.serverTrust];
  // 3.信任服务器证书
  completionHandler(0,credential);
  }
  }
  @end

demo地址：https://github.com/SFOC/HTTPS-