a href="http://developer.apple.com/library/ios/#documentation/Cocoa/Reference/Foundation/Classes/NSMutableURLRequest_Class/Reference/Reference.html"> http://developer.apple.com/library/ios/#documentation/Cocoa/Reference/Foundation/Classes/NSMutableURLRequest_Class/Reference/Reference.html
setValue:forHTTPHeaderField:でHTTPリクエストヘッダに独自フィールドを追加できるか?
上記のクラスの親クラス ↓
http://developer.apple.com/library/ios/#documentation/Cocoa/Reference/Foundation/Classes/NSURLRequest_Class/Reference/Reference.html