youtube api v3 - get videos from a public playlist. with out using api key

Youtube V2 where this code use to list top 50 videos from the play list

        var ytURL = "http://gdata.youtube.com/feeds/api/playlists/PLgtnUFn0ROBBPO2nC-bduEDDlxikKwZ6R?v=2&alt=json&callback=?&max-results=50";    var thumbBase = "http://img.youtube.com/vi/";    $.getJSON(ytURL, function (data) {            $.each(data.feed.entry, function (i, item) {                var itemTitle = item.title.$t; // Title of the video                var itemdescription = item.media$group.media$description.$t; //Description of the Video                itemdescription = itemdescription.replace(/"/g, "");                var itemdate = item.published.$t;                var fulldate = new Date(itemdate).toLocaleDateString();                 var yobject = { 'title': itemTitle, 'description': itemdescription, 'gdate': itemdate };               localStorage.setItem(videoID, JSON.stringify(yobject));            });

Same code is not working now, since google update the youtube apis

i have referred the youtube documentation,after seeing that i came to know to use like this

https://www.googleapis.com/youtube/v3/playlistItems?part=snippet&playlistId=PLgtnUFn0ROBBPO2nC-bduEDDlxikKwZ6R&key={YOUR_KEY_HERE}&maxResults=50

Problem is, There was public : playlist id "PLgtnUFn0ROBBPO2nC-bduEDDlxikKwZ6R" here.

i want to list all the videos from the playlist without using API key..

how can i access this...

suggest me to how can i overcome from this solution