private function ect(): array
    {
        $ect = "max-age={$this->security['ect']['max-age']}";
        if ($this->security['ect']['enforce']) {
            $ect .= ', enforce';
        }

        if (! empty($this->security['ect']['report-uri'])) {
            $ect .= sprintf(', report-uri="%s"', $this->security['ect']['report-uri']);
        }

        return ['Expect-CT' => $ect];
    }