title: NSURLSessionConfiguration HTTPAdditionalHeaders not set
body: <p>Authorization header is set in <code>NSURLSessionConfiguration</code>, however it is not attached to <code>NSURLSessionDataTask</code>. Is this a bug in <code>Foundation framework</code>?</p>
  
  <pre><code>NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration defaultSessionConfiguration];
  [configuration setHTTPAdditionalHeaders:@{@"Authorization":@"123"}];
  
  // Initialize session with NSURLSessionConfiguration
  NSURLSession *session = [NSURLSession sessionWithConfiguration:configuration];
  NSMutableURLRequest *request = [[NSMutableURLRequest alloc] initWithURL:url];
  NSURLSessionDataTask *sessionTask = [session dataTaskWithRequest:request
                                          completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
  }];
  
  [sessionTask resume];
  </code></pre>