I literally used this guide to set me up:
https://developers.google.com/youtube/v3...ng-started
First, I enabled the YouTube Data API, v3.
Then, after that was enabled, I created an API key. This is what you will put into the "key" field in the login_client.py file that has been mentioned elsewhere.
Then, I created an OAuth 2.0 ID. The "Client ID" value goes into the "id" field in the login_client.py file, and the "Client Secret" goes into the "secret" field.
Please note, when creating the API and OAuth keys, to use a name that you'd recognize. For instance, I used "Kodi YouTube (wad)" for mine, so I know if I'm hitting the right thing or not.
I'm using Kodi 15, so I just commented out the three old values using # in front, and added (in the same order) my new values. If you're using a different version of Kodi, then find that version and replace those values. Don't try to create a new product, it's not worth the hassle. Then I zipped up the entire folder with no compression and dropped it into a place my Kodi install could access, and then installed an add-on from a zip file (make sure to uninstall the one from repo first).
The last thing you'll want to do is set plugins to prompt for update, otherwise (like me) you'll possibly wake up and find the plugin updated over Christmas and blew away your fix.
Hope that helps!