Implementing TOTP Using Google Authenticator in Java

<!-- https://mvnrepository.com/artifact/com.warrenstrange/googleauth -->
		<dependency>
			<groupId>com.warrenstrange</groupId>
			<artifactId>googleauth</artifactId>
			<version>1.1.5</version>
		</dependency>


		<!-- https://mvnrepository.com/artifact/com.google.zxing/javase -->
		<dependency>
			<groupId>com.google.zxing</groupId>
			<artifactId>javase</artifactId>
			<version>3.3.3</version>
		</dependency>

final GoogleAuthenticator gAuth = new GoogleAuthenticator();	
final GoogleAuthenticatorKey googleAuthkey = gAuth.createCredentials();
String key = googleAuthkey.getKey();

URI uri = new URI("otpauth", "totp", "/" + issuer + ":" + account, "secret=" + secret + "&issuer=" + issuer,null);
uri.toASCIIString();

public Map<String, String> qrCodeGeneration(Users user) throws URISyntaxException, WriterException, IOException {
		String key = getTwoFactorKey(user);
		String filePath = qrCodeLocation + File.separator + user.getId() + ".png";
		String charset = "UTF-8"; // or "ISO-8859-1"
		Map<EncodeHintType, ErrorCorrectionLevel> hintMap = new EnumMap<>(EncodeHintType.class);
		hintMap.put(EncodeHintType.ERROR_CORRECTION, ErrorCorrectionLevel.L);
		String keyUri = generateKeyUri("test.com", user.getEmailId(), key);
		String qrCodeData = keyUri;
		String base64Image = createQRCode(qrCodeData, filePath, charset, hintMap, 200, 200);
		Map<String, String> map = new HashMap<>();
		map.put("fileName", user.getId() + ".png");
		map.put("key", key);
		map.put("base64Image", base64Image);
		map.put("verificationToken", verificationToken.getToken());
		return map;
	}

//Configure the Google Authenticator App by scanning the following QR code image
private static String createQRCode(String qrCodeData, String filePath, String charset,
			@SuppressWarnings("rawtypes") Map hintMap, int qrCodeheight, int qrCodewidth)
			throws WriterException, IOException {
		@SuppressWarnings("unchecked")
		BitMatrix matrix = new MultiFormatWriter().encode(new String(qrCodeData.getBytes(charset), charset),
				BarcodeFormat.QR_CODE, qrCodewidth, qrCodeheight, hintMap);
		File file = new File(filePath);
		MatrixToImageWriter.writeToPath(matrix, filePath.substring(filePath.lastIndexOf('.') + 1), file.toPath());
		Encoder encoder = Base64.getEncoder();
		String base64Image = encoder.encodeToString(Files.readAllBytes(file.toPath()));
		// using PosixFilePermission to set file permissions 777
		Set<PosixFilePermission> perms = new HashSet<>();
		// add owners permission
		perms.add(PosixFilePermission.OWNER_READ);
		perms.add(PosixFilePermission.OWNER_WRITE);
		// add group permissions
		perms.add(PosixFilePermission.GROUP_READ);
		perms.add(PosixFilePermission.GROUP_WRITE);
		// add others permissions
		perms.add(PosixFilePermission.OTHERS_READ);
		Files.setPosixFilePermissions(Paths.get(file.toString()), perms);
		logger.info("2FA QR code generated");
		return "data:image/png;base64," + base64Image;
}

//To check whether generated google auth key is authenticated or not
public boolean performAuthentication(String value, Users user) {
        Integer totp = Integer.valueOf((value.equals("") ? "-1" : value));
        boolean unused = isUnusedPassword(totp, windowSize.get());
        boolean matches = gAuth.authorize(user.getGoogle2FaAuthKey(), totp);
        return (unused && matches);
}

private long KEY_VALIDATION_INTERVAL_MS = TimeUnit.SECONDS.toMillis(30);

private boolean isUnusedPassword(int password, int windowSize) {
        long now = new Date().getTime();
        long timeslotNow = now / KEY_VALIDATION_INTERVAL_MS;
        int forwardTimeslots = ((windowSize - 1) / 2);
        long timeslotThen = lastVerifiedTime / KEY_VALIDATION_INTERVAL_MS;
        if (password != lastUsedPassword || timeslotNow > timeslotThen + forwardTimeslots) {
            lastUsedPassword = password;
            lastVerifiedTime = now;
            return true;
        }
        return false;
}