Objective c 如何使用amazon预签名URL

我正在尝试使用预先签名的URL从Amazon下载图像。这是代码，但一定是缺少了什么，并且图像没有显示出来。提前谢谢

//Set up the request
S3GetPreSignedURLRequest * request = [[S3GetPreSignedURLRequest alloc] init];
request.bucket = @"a";
request.key = @"b";
request.contentType = @"image/jpeg";
request.httpVerb = @"GET"; 

//set credential
AmazonCredentials * credentials = [[AmazonCredentials alloc] initWithAccessKey:ACCESS_KEY withSecretKey:SECRET_KEY];
request.credentials = credentials;

//set expire
NSDateComponents *components = [[[NSDateComponents alloc] init] autorelease];
[components setHour:1];
NSDate * oneHourFromNow = [[NSCalendar currentCalendar] dateByAddingComponents:components toDate:[NSDate date] options:0];

request.expires = oneHourFromNow;

//get the presigned URL
NSURL * url = [[Constants s3] getPreSignedURL: request];

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过期

需要UTC时间，而不是本地时间。

如果有人正在寻找使用Amazon CloudFront的预签名URL，您可能会找到。

您是否能够解决此问题。因为我面临着同样的问题