STSFederationToken过期时间不起作用

根据教程，我的 setFederationTokenGetter是这么写的，测试正确，能够正确下载文件， 我原先以为是 OSSservice判断 token 过期后，才会回调这个方法重新获取新的 token。
但是现在是 每次点击按钮下载文件，系统都会进入这个方法重新向业务服务器申请新token, 不管 expiration过不过期， 难道token网络获取不是写在这个block中？或者expiration设置有误？  哪位大神帮我解答下这个问题。非常感谢！
[ossService setFederationTokenGetter :^{
//获取新的token
         NSURL * url = [ NSURL URLWithString :@"http://localhost:9080/list/token/" ];
         NSURLRequest *urlRequest = [ NSURLRequest requestWithURL :url cachePolicy :NSURLRequestReloadIgnoringLocalAndRemoteCacheData timeoutInterval : 10.0f ]; //maximal timeout is 30s

        NSOperationQueue *queue = [[NSOperationQueue alloc ] init ];
        [ NSURLConnection sendAsynchronousRequest:urlRequest queue:queue completionHandler:^( NSURLResponse *response, NSData *data, NSError *connectionError) {
             if ([data length] > 0 && connectionError == nil) {
               object = [ NSJSONSerialization JSONObjectWithData:data
                                                                         options: kNilOptions
                                                                           error: nil];



                 NSLog( @"Successfully ");
            } else if ([data length] == 0 && connectionError == nil){
                 NSLog (@"Nothing was downloaded." );
            } else if (connectionError != nil){
                 NSLog( @"Error happened = %@",connectionError);
            }
        }];

         NSDictionary *tempfederation=[ object objectForKey: @"FederationToken"];
             accessKey = [tempfederation valueForKey: @"accesskeyid"];
             secretKey = [tempfederation valueForKey: @"accesssecret"];
             demotoken = [tempfederation valueForKey: @"securitytoken"];
         demoExpiration =  [ NSNumber numberWithInt:[[tempfederation   valueForKey: @"expiration"] intValue]];
        OSSFederationToken   *federationToken = [[OSSFederationToken alloc ] initWithAk :accessKey sk :secretKey tempToken :demotoken expiration :demoExpiration ];

             return federationToken;


      
    }];