OneLogin_Saml2_Utils::extractOriginalQueryParam PHP Method

    public static function extractOriginalQueryParam($name)
    {
        $index = strpos($_SERVER['QUERY_STRING'], $name . '=');
        $substring = substr($_SERVER['QUERY_STRING'], $index + strlen($name) + 1);
        $end = strpos($substring, '&');
        return $end ? substr($substring, 0, strpos($substring, '&')) : $substring;
    }

 /**
  * Checks if the Logout Request recieved is valid.
  *
  * @return boolean If the Logout Request is or not valid
  */
 public function isValid($retrieveParametersFromServer = false)
 {
     $this->_error = null;
     try {
         $dom = new DOMDocument();
         $dom = OneLogin_Saml2_Utils::loadXML($dom, $this->_logoutRequest);
         $idpData = $this->_settings->getIdPData();
         $idPEntityId = $idpData['entityId'];
         if ($this->_settings->isStrict()) {
             $security = $this->_settings->getSecurityData();
             if ($security['wantXMLValidation']) {
                 $res = OneLogin_Saml2_Utils::validateXML($dom, 'saml-schema-protocol-2.0.xsd', $this->_settings->isDebugActive());
                 if (!$res instanceof DOMDocument) {
                     throw new Exception("Invalid SAML Logout Request. Not match the saml-schema-protocol-2.0.xsd");
                 }
             }
             $currentURL = OneLogin_Saml2_Utils::getSelfRoutedURLNoQuery();
             // Check NotOnOrAfter
             if ($dom->documentElement->hasAttribute('NotOnOrAfter')) {
                 $na = OneLogin_Saml2_Utils::parseSAML2Time($dom->documentElement->getAttribute('NotOnOrAfter'));
                 if ($na <= time()) {
                     throw new Exception('Timing issues (please check your clock settings)');
                 }
             }
             // Check destination
             if ($dom->documentElement->hasAttribute('Destination')) {
                 $destination = $dom->documentElement->getAttribute('Destination');
                 if (!empty($destination)) {
                     if (strpos($destination, $currentURL) === false) {
                         throw new Exception("The LogoutRequest was received at {$currentURL} instead of {$destination}");
                     }
                 }
             }
             $nameId = $this->getNameId($dom, $this->_settings->getSPkey());
             // Check issuer
             $issuer = $this->getIssuer($dom);
             if (!empty($issuer) && $issuer != $idPEntityId) {
                 throw new Exception("Invalid issuer in the Logout Request");
             }
             if ($security['wantMessagesSigned']) {
                 if (!isset($_GET['Signature'])) {
                     throw new Exception("The Message of the Logout Request is not signed and the SP require it");
                 }
             }
         }
         if (isset($_GET['Signature'])) {
             if (!isset($_GET['SigAlg'])) {
                 $signAlg = XMLSecurityKey::RSA_SHA1;
             } else {
                 $signAlg = $_GET['SigAlg'];
             }
             if ($retrieveParametersFromServer) {
                 $signedQuery = 'SAMLRequest=' . OneLogin_Saml2_Utils::extractOriginalQueryParam('SAMLRequest');
                 if (isset($_GET['RelayState'])) {
                     $signedQuery .= '&RelayState=' . OneLogin_Saml2_Utils::extractOriginalQueryParam('RelayState');
                 }
                 $signedQuery .= '&SigAlg=' . OneLogin_Saml2_Utils::extractOriginalQueryParam('SigAlg');
             } else {
                 $signedQuery = 'SAMLRequest=' . urlencode($_GET['SAMLRequest']);
                 if (isset($_GET['RelayState'])) {
                     $signedQuery .= '&RelayState=' . urlencode($_GET['RelayState']);
                 }
                 $signedQuery .= '&SigAlg=' . urlencode($signAlg);
             }
             if (!isset($idpData['x509cert']) || empty($idpData['x509cert'])) {
                 throw new Exception('In order to validate the sign on the Logout Request, the x509cert of the IdP is required');
             }
             $cert = $idpData['x509cert'];
             $objKey = new XMLSecurityKey(XMLSecurityKey::RSA_SHA1, array('type' => 'public'));
             $objKey->loadKey($cert, false, true);
             if ($signAlg != XMLSecurityKey::RSA_SHA1) {
                 try {
                     $objKey = OneLogin_Saml2_Utils::castKey($objKey, $signAlg, 'public');
                 } catch (Exception $e) {
                     throw new Exception('Invalid signAlg in the recieved Logout Request');
                 }
             }
             if (!$objKey->verifySignature($signedQuery, base64_decode($_GET['Signature']))) {
                 throw new Exception('Signature validation failed. Logout Request rejected');
             }
         }
         return true;
     } catch (Exception $e) {
         $this->_error = $e->getMessage();
         $debug = $this->_settings->isDebugActive();
         if ($debug) {
             echo $this->_error;
         }
         return false;
     }
 }