Classes/Controller/ConfigurationController.php
protected function writeToLocalconf($key, array $config)
    {
        /** @var $objectManager \TYPO3\CMS\Extbase\Object\ObjectManager */
        $objectManager = GeneralUtility::makeInstance(\TYPO3\CMS\Extbase\Object\ObjectManager::class);
        /** @var $configurationManager \TYPO3\CMS\Core\Configuration\ConfigurationManager */
        $configurationManager = $objectManager->get(\TYPO3\CMS\Core\Configuration\ConfigurationManager::class);
        return $configurationManager->setLocalConfigurationValueByPath('EXT/extConf/' . $key, serialize($config));
    }
protected function writeToLocalconf($key, array $config)
    {
        /** @var $objectManager \TYPO3\CMS\Extbase\Object\ObjectManager */
        $objectManager = GeneralUtility::makeInstance(\TYPO3\CMS\Extbase\Object\ObjectManager::class);
        /** @var $configurationManager \TYPO3\CMS\Core\Configuration\ConfigurationManager */
        $configurationManager = $objectManager->get(\TYPO3\CMS\Core\Configuration\ConfigurationManager::class);
        return $configurationManager->setLocalConfigurationValueByPath('EXT/extConf/' . $key, serialize($config));
    }
Writes a configuration line to AdditionalConfiguration.php.
We don't use the <code>tx_install</code> methods as they add unneeded
comments at the end of the file.

@param string $key
@param array $config
@return bool