private function retrieveConfigurationValues(array $options): array
    {
        $outputValues = [];

        foreach ($options as $option) {
            $value = getenv($option);

            // value was not retrieved => fail
            if ($value === false) {
                throw new \RuntimeException(sprintf('%s environment variable must be defined', $option));
            }

            $outputValues[Inflector::camelize(mb_strtolower($option))] = $value;
        }

        return $outputValues;
    }