Cocoa NSURLCache未在osx中缓存https

问题是NSURLCache没有缓存https url请求。我查过了

    [NSURLCache sharedURLCache];
    NSURLRequest *request = [[NSURLRequest alloc] initWithURL:[NSURL URLWithString:@"https://fbcdn-sphotos-f-a.akamaihd.net/hphotos-ak-prn2/703666_3663940170939_253924330_o.jpg"]];

    NSCachedURLResponse *cachedResponse = [[NSURLCache sharedURLCache] cachedResponseForRequest:request];
    NSLog(cachedResponse ? @"Cached response found!" : @"No cached response found.");

    [NSURLConnection sendSynchronousRequest:request returningResponse:NULL error:NULL];

现在我让NSURLConnection加载文件，关闭我的应用程序，然后再次运行。它始终显示未找到缓存响应。但如果我只是在同一个url中将https更改为http，它就工作了，缓存被保存

你知道如何让它也保存https吗