如何通过AWSBasicSessionCredentialsProvider上传文件？

Question

    AWSBasicSessionCredentialsProvider * provider = [[AWSBasicSessionCredentialsProvider alloc] initWithAccessKey:weakSelf.awsCredential.key secretKey:weakSelf.awsCredential.secret sessionToken:weakSelf.awsCredential.token];

    AWSEndpoint *endpoint = [[AWSEndpoint alloc] initWithURLString:@"https://s3.amazonaws.com"];
    AWSServiceConfiguration *config = [[AWSServiceConfiguration alloc] initWithRegion:AWSRegionUSEast1 endpoint:endpoint credentialsProvider:provider];

    config.timeoutIntervalForRequest  = 30;
    config.timeoutIntervalForResource = 30;
    config.maxRetryCount = 1;
    AWSServiceManager *serviceManager  = [AWSServiceManager defaultServiceManager];
    serviceManager.defaultServiceConfiguration = config;



    AWSS3TransferUtility *transferUtility = [AWSS3TransferUtility defaultS3TransferUtility];

    AWSS3TransferUtilityUploadExpression *expression = [AWSS3TransferUtilityUploadExpression new];
    expression.progressBlock = uploadProgress;
    NSString *bucket = [AWSS3Configure sharedManager].bucketName;
    NSString *key = objectKey;
    NSString *contentType = @"image/jpeg";

    AWSTask<AWSS3TransferUtilityUploadTask *> *task = [transferUtility uploadData:dataToUpload bucket:bucket key:key contentType:contentType expression:expression completionHandler:^(AWSS3TransferUtilityUploadTask * _Nonnull task, NSError * _Nullable error) {
            NSString *fileUrl = [[AWSS3Configure sharedManager].hostUrl stringByAppendingFormat:@"/%@",objectKey];
            if (!error) {
                [subscriber sendNext:fileUrl];
                [subscriber sendCompleted];
                YSLog(@"Upload to %@ success", fileUrl);
            } else {
                [subscriber sendError:error];

                YSLog(@"Upload to %@ failed", fileUrl);
            }
        }];

  

错误Domain = com.amazonaws.AWSS3TransferUtilityErrorDomain Code = 2“（null）”UserInfo = {Server = AmazonS3，Transfer-Encoding = Identity，Connection = close，Content-Type = application / xml，Date = Mon，Jun Jun 2017 06:37:51 GMT，x-amz-request-id = A5E32BD17E6558F5，

这是错误的。怎么做？