public function nonce(string $directive = 'script-src', string $nonce = '') : string
{
$ruleKeys = \array_keys($this->policies);
if (!\in_array($directive, $ruleKeys)) {
return '';
}
if (empty($nonce)) {
$nonce = Base64::encode(\random_bytes(18));
}
$this->policies[$directive]['nonces'][] = $nonce;
return $nonce;
}