Jose\Object\SignatureInterface::getProtectedHeader PHP Method

    public function getProtectedHeader($key);

 /**
  * @param \Jose\Object\SignatureInterface $signature
  *
  * @throws \InvalidArgumentException
  */
 private function checkB64HeaderAndCrit(Object\SignatureInterface $signature)
 {
     if (!$signature->hasProtectedHeader('b64')) {
         return;
     }
     Assertion::true($signature->hasProtectedHeader('crit'), 'The protected header parameter "crit" is mandatory when protected header parameter "b64" is set.');
     Assertion::isArray($signature->getProtectedHeader('crit'), 'The protected header parameter "crit" must be an array.');
     Assertion::inArray('b64', $signature->getProtectedHeader('crit'), 'The protected header parameter "crit" must contain "b64" when protected header parameter "b64" is set.');
 }