OneLogin_Saml2_Settings::getSPkey PHP Method

    public function getSPkey()
    {
        $key = null;
        if (isset($this->_sp['privateKey']) && !empty($this->_sp['privateKey'])) {
            $key = $this->_sp['privateKey'];
        } else {
            $keyFile = $this->_paths['cert'] . 'sp.key';
            if (file_exists($keyFile)) {
                $key = file_get_contents($keyFile);
            }
        }
        return $key;
    }

 /**
  * Decrypts the Assertion (DOMDocument)
  *
  * @param string $dom DomDocument
  *
  * @throws Exception
  * @return DOMDocument Decrypted Assertion
  */
 private function _decryptAssertion($dom)
 {
     $pem = $this->_settings->getSPkey();
     if (empty($pem)) {
         throw new Exception("No private key available, check settings");
     }
     $objenc = new XMLSecEnc();
     $encData = $objenc->locateEncryptedData($dom);
     if (!$encData) {
         throw new Exception("Cannot locate encrypted assertion");
     }
     $objenc->setNode($encData);
     $objenc->type = $encData->getAttribute("Type");
     if (!($objKey = $objenc->locateKey())) {
         throw new Exception("Unknown algorithm");
     }
     $key = null;
     if ($objKeyInfo = $objenc->locateKeyInfo($objKey)) {
         if ($objKeyInfo->isEncrypted) {
             $objencKey = $objKeyInfo->encryptedCtx;
             $objKeyInfo->loadKey($pem, false, false);
             $key = $objencKey->decryptKey($objKeyInfo);
         }
     }
     if (empty($objKey->key)) {
         $objKey->loadKey($key);
     }
     $decrypt = $objenc->decryptNode($objKey, true);
     if ($decrypt instanceof DOMDocument) {
         return $decrypt;
     } else {
         return $decrypt->ownerDocument;
     }
 }