'In google calendar, you can have multiple calendar. But only one is
the \'primary\' one. This Calendar identifier is \'primary\'.'

def get_calendar_primary_id(self):

    params = {'fields': 'id', 'access_token': self.get_token()}
    headers = {'Content-type': 'application/json', 'Accept': 'text/plain'}
    url = '/calendar/v3/calendars/primary'
    try:
        (status, content, ask_time) = self.env['google.service']._do_request(url, params, headers, type='GET')
    except urllib2.HTTPError as e:
        if (e.code == 401):
            error_msg = _('Your    token    is    invalid    or    has    been    revoked    !')
            self.env.user.write({'google_calendar_token': False, 'google_calendar_token_validity': False})
            self.env.cr.commit()
            raise self.env['res.config.settings'].get_config_warning(error_msg)
        raise
    return (status_response(status), (content['id'] or False), ask_time)
