/** Delete all the expired tokens
*
*/
private function cleanUp()
{
$tokens = new OauthTokens();
$where = array();
$where[] = $tokens->getAdapter()->quoteInto('service = ?', 'yahooAccess');
$where[] = $tokens->getAdapter()->quoteInto('expires <= ?', $this->_now);
$tokens->delete($where);
}
