Illuminate\Routing\UrlGenerator::getScheme PHP Method

    protected function getScheme($secure)
    {
        if (is_null($secure)) {
            if (is_null($this->cachedSchema)) {
                $this->cachedSchema = $this->forceSchema ?: $this->request->getScheme() . '://';
            }
            return $this->cachedSchema;
        }
        return $secure ? 'https://' : 'http://';
    }