in order to enable authentification with google acounts you have to change: $tutos[authtype] in config.php to google.
In preparation to this you have to define the google email adresses on the users in the user settings dialog. (Section custom fields / google email)
you also have to set the values for
$tutos['google_client'] = 'xxxxxxxxxxxx.apps.googleusercontent.com'; $tutos['google_secret'] = 'xxxxxxxxxxxxxxxxxxxxxxxx';
in your config.php
The correct values are avaiable after adding a project in https://code.google.com/apis/console/ and defining a client id for web applications.
This feature is currently (22 February 2013) in early testing in the development branch of TUTOS.