Twitter Api 1.1 Bad Authentication

Question

I have these code in Twitter Api v 1

$url = get_data("http://api.twitter.com/1/users/show.json?screen_name=".$name);
$xml = json_decode($url, true);
$id = $xml[0][id];
$av = $xml[0][profile_image_url];

But Api 1 is closed and i have to update to Api 1.1, But Api 1.1 uses Authentication, And i can not get the Right way to Solve it.

Please tell me all steps and Code to replace it.