使用NSURLSession请求需要AD认证的HTTPS服务器

关键代码：使用后台下载PDF文件

- (void)startDownloadPDF{
    
    NSURLSession *session = [self session];
    NSString *downloadURLString = _fileURL;
    NSURL *downloadURL = [NSURL URLWithString:[kGlobal getEncodeUrl:downloadURLString]];
    
　　//使用NSMutableURLRequest进行AD认证
    NSMutableURLRequest *req = [NSMutableURLRequest requestWithURL:downloadURL];
    
    NSString *authString = [[[NSString stringWithFormat:@"%@:%@", kGlobal.userInfo.sAccount, kGlobal.userInfo.sPassword] dataUsingEncoding:NSUTF8StringEncoding] base64EncodedString];
    
    authString = [NSString stringWithFormat: @"Basic %@", authString];
    
    [req setValue:authString forHTTPHeaderField:@"Authorization"];
    
    NSURLSessionDownloadTask *task = [session downloadTaskWithRequest:req];
    
    //执行resume 保证开始了任务
    [task resume];
    
}

//后台会话(保证只有一个后台会话)
-(NSURLSession *)session {
    static NSURLSession *session;
    static dispatch_once_t token;
    dispatch_once(&token, ^{
        //后台下载
        NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration backgroundSessionConfigurationWithIdentifier:@"rich"];
        configuration.discretionary = YES;
        
        //使用配置的NSURLSessionConfiguration获取NSSession，并且设置委托
        session = [NSURLSession sessionWithConfiguration:configuration delegate:self delegateQueue:nil];
    });
    
    return session;
}

//HTTPS认证
- (void)URLSession:(NSURLSession *)session didReceiveChallenge:(NSURLAuthenticationChallenge *)challenge completionHandler:(void (^)(NSURLSessionAuthChallengeDisposition, NSURLCredential * _Nullable))completionHandler{
    
    NSURLSessionAuthChallengeDisposition disposition = NSURLSessionAuthChallengePerformDefaultHandling;
    __block NSURLCredential *credential = nil;
    
    if ([challenge.protectionSpace.authenticationMethod isEqualToString:NSURLAuthenticationMethodServerTrust]) {
        credential = [NSURLCredential credentialForTrust:challenge.protectionSpace.serverTrust];
        if (credential) {
            disposition = NSURLSessionAuthChallengeUseCredential;
        } else {
            disposition = NSURLSessionAuthChallengePerformDefaultHandling;
        }
    } else {
        disposition = NSURLSessionAuthChallengePerformDefaultHandling;
    }
    
    if (completionHandler) {
        completionHandler(disposition, credential);
    }
}

//打印下载过程，下载的百分比
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask
      didWriteData:(int64_t)bytesWritten
 totalBytesWritten:(int64_t)totalBytesWritten
totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite {
    float percent = (float)totalBytesWritten/totalBytesExpectedToWrite;
    NSLog(@"%f",percent);
}

//下载完成之后的文件存储在临时目录中，下载完成之后，转移文件的目录
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask
didFinishDownloadingToURL:(NSURL *)location {
//    NSString *dirPath = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) firstObject];
//    NSString *path = [dirPath stringByAppendingPathComponent:@"1.mp3"];
//    
//    NSFileManager *manager = [NSFileManager defaultManager];
//    if ([manager fileExistsAtPath:path isDirectory:NO]) {
//        [manager removeItemAtPath:path error:nil];
//    }
//    
//    [manager moveItemAtPath:[location path] toPath:path error:nil];
}

//任务结束
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task
didCompleteWithError:(NSError *)error {
    NSLog(@"%s:%@",__func__,error);
    if (error == NULL) {
        self.rightButton.enabled = YES;
    }
}