  private String buildRedirectAuthnRequest(AuthnRequestType authnRequest, String relayState, boolean sign,
                                           PrivateKey key, Algorithm algorithm) throws SAMLException {
    try {
      byte[] xml = marshallToBytes(PROTOCOL_OBJECT_FACTORY.createAuthnRequest(authnRequest), AuthnRequestType.class);
      String encodedResult = deflateAndEncode(xml);
      String parameters = "SAMLRequest=" + URLEncoder.encode(encodedResult, "UTF-8");
      if (relayState != null) {
        parameters += "&RelayState=" + URLEncoder.encode(relayState, "UTF-8");
      }

      if (sign && key != null && algorithm != null) {
        Signature signature;
        parameters += "&SigAlg=" + URLEncoder.encode(algorithm.uri, "UTF-8");
        signature = Signature.getInstance(algorithm.name);
        signature.initSign(key);
        signature.update(parameters.getBytes(StandardCharsets.UTF_8));

        String signatureParameter = Base64.getEncoder().encodeToString(signature.sign());
        parameters += "&Signature=" + URLEncoder.encode(signatureParameter, "UTF-8");
      }

      return parameters;
    } catch (Exception e) {
      // Not possible but freak out
      throw new SAMLException(e);
    }
  }
The software processes an XML document that can contain XML entities with URIs that resolve to documents outside of the intended sphere of control, causing the product to embed incorrect documents into its output.