Google app

If you don't have one, create a new project

../img/oauth-1.png

Go to Library and enable GMAIL API

../img/oauth-2.png
../img/oauth-3.png
../img/oauth-4.png

If you don't have it, configure the consent screen

../img/oauth-5.png
../img/oauth-6.png
../img/oauth-7.png

Click Add or Remove Scopes and search gmail.send

../img/oauth-8.png
../img/oauth-9.png

Click on + CREATE CREDENTIALS and select OAuth client ID

../img/oauth-10.png

Select "Web Application" as the type.

On Authorized redirect URIs add your xBit installation host + /about.php
(e.g., http://yourdomain.xbit/about.php)

Copy the Client ID and Secret

../img/oauth-11.jpg

Configuring in xBit