GuzzleHttp\Client::configureDefaults PHP Method

    private function configureDefaults(array $config)
    {
        $defaults = ['allow_redirects' => RedirectMiddleware::$defaultSettings, 'http_errors' => true, 'decode_content' => true, 'verify' => true, 'cookies' => false];
        // Use the standard Linux HTTP_PROXY and HTTPS_PROXY if set.
        // We can only trust the HTTP_PROXY environment variable in a CLI
        // process due to the fact that PHP has no reliable mechanism to
        // get environment variables that start with "HTTP_".
        if (php_sapi_name() == 'cli' && getenv('HTTP_PROXY')) {
            $defaults['proxy']['http'] = getenv('HTTP_PROXY');
        }
        if ($proxy = getenv('HTTPS_PROXY')) {
            $defaults['proxy']['https'] = $proxy;
        }
        if ($noProxy = getenv('NO_PROXY')) {
            $cleanedNoProxy = str_replace(' ', '', $noProxy);
            $defaults['proxy']['no'] = explode(',', $cleanedNoProxy);
        }
        $this->config = $config + $defaults;
        if (!empty($config['cookies']) && $config['cookies'] === true) {
            $this->config['cookies'] = new CookieJar();
        }
        // Add the default user-agent header.
        if (!isset($this->config['headers'])) {
            $this->config['headers'] = ['User-Agent' => default_user_agent()];
        } else {
            // Add the User-Agent header if one was not already set.
            foreach (array_keys($this->config['headers']) as $name) {
                if (strtolower($name) === 'user-agent') {
                    return;
                }
            }
            $this->config['headers']['User-Agent'] = default_user_agent();
        }
    }