How to ask for permissions?

How do I create a dialog l开发者_开发知识库ike the following one in Objective-C? Mac OS X authorization http://img340.imageshack.us/img340/5900/screenshot20100522at153.png

I'm quite new to Objective-C, and I need root access to a file in the /etc directory.

Thanks!! Yvan

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Check out Authorization Concepts and the code sample: BetterAuthorizationSample.