First you make an instance of the tslib_fe class like:
$GLOBALS['TSFE'] = t3lib_div::makeInstance('tslib_fe',
        $GLOBALS['TYPO3_CONF_VARS'],
        t3lib_div::_GP('id'),
        t3lib_div::_GP('type'),
        and more variables if you want
);
(please check your incoming values 😉

Do some other stuff (check if you need this)
$GLOBALS['TSFE']->connectToMySQL();
$GLOBALS['TSFE']->initFEuser();
$GLOBALS['TSFE']->determineId();
$GLOBALS['TSFE']->getCompressedTCarray();
$GLOBALS['TSFE']->initTemplate();
$GLOBALS['TSFE']->getConfigArray();

And you can get the configuration at:
$configuration =
$GLOBALS['TSFE']->tmpl->setup['plugin.']['tx_yourextension_controller.'];