/**
* @param \Jose\Object\JWEInterface $jwe
*
* @return \Jose\Algorithm\ContentEncryptionAlgorithmInterface
*/
private function getContentEncryptionAlgorithm(Object\JWEInterface $jwe)
{
$algorithm = null;
foreach ($jwe->getRecipients() as $recipient) {
$complete_headers = array_merge($jwe->getSharedProtectedHeaders(), $jwe->getSharedHeaders(), $recipient->getHeaders());
Assertion::keyExists($complete_headers, 'enc', 'Parameter "enc" is missing.');
if (null === $algorithm) {
$algorithm = $complete_headers['enc'];
} else {
Assertion::eq($algorithm, $complete_headers['enc'], 'Foreign content encryption algorithms are not allowed.');
}
}
$content_encryption_algorithm = $this->getJWAManager()->getAlgorithm($algorithm);
Assertion::isInstanceOf($content_encryption_algorithm, Algorithm\ContentEncryptionAlgorithmInterface::class, sprintf('The content encryption algorithm "%s" is not supported or not a content encryption algorithm instance.', $algorithm));
return $content_encryption_algorithm;
}