private void rotateTokens(HttpServletRequest request) {
    HttpSession session = request.getSession(true);

    /** rotate master token * */
    String tokenFromSession = null;

    try {
      tokenFromSession = RandomGenerator.generateRandomId(getPrng(), getTokenLength());
    } catch (Exception e) {
      throw new RuntimeException(
          String.format("unable to generate the random token - %s", e.getLocalizedMessage()), e);
    }

    session.setAttribute(getSessionKey(), tokenFromSession);

    /** rotate page token * */
    if (isTokenPerPageEnabled()) {
      @SuppressWarnings("unchecked")
      Map<String, String> pageTokens =
          (Map<String, String>) session.getAttribute(CsrfGuard.PAGE_TOKENS_KEY);

      try {
        pageTokens.put(
            request.getRequestURI(), RandomGenerator.generateRandomId(getPrng(), getTokenLength()));
      } catch (Exception e) {
        throw new RuntimeException(
            String.format("unable to generate the random token - %s", e.getLocalizedMessage()), e);
      }
    }
  }
  public String getTokenValue(HttpServletRequest request, String uri) {
    String tokenValue = null;
    HttpSession session = request.getSession(false);

    if (session != null) {
      if (isTokenPerPageEnabled()) {
        @SuppressWarnings("unchecked")
        Map<String, String> pageTokens =
            (Map<String, String>) session.getAttribute(CsrfGuard.PAGE_TOKENS_KEY);

        if (pageTokens != null) {
          if (isTokenPerPagePrecreate()) {
            createPageToken(pageTokens, uri);
          }
          tokenValue = pageTokens.get(uri);
        }
      }

      if (tokenValue == null) {
        tokenValue = (String) session.getAttribute(getSessionKey());
      }
    }

    return tokenValue;
  }
  /**
   * Create page token if it doesn't exist.
   *
   * @param pageTokens A map of tokens. If token doesn't exist it will be added.
   * @param uri The key for the tokens.
   */
  private void createPageToken(Map<String, String> pageTokens, String uri) {

    if (pageTokens == null) return;

    /** create token if it does not exist * */
    if (pageTokens.containsKey(uri)) return;
    try {
      pageTokens.put(uri, RandomGenerator.generateRandomId(getPrng(), getTokenLength()));
    } catch (Exception e) {
      throw new RuntimeException(
          String.format("unable to generate the random token - %s", e.getLocalizedMessage()), e);
    }
  }
  private void verifyPageToken(HttpServletRequest request) throws CsrfGuardException {
    HttpSession session = request.getSession(true);
    @SuppressWarnings("unchecked")
    Map<String, String> pageTokens =
        (Map<String, String>) session.getAttribute(CsrfGuard.PAGE_TOKENS_KEY);

    String tokenFromPages = (pageTokens != null ? pageTokens.get(request.getRequestURI()) : null);
    String tokenFromSession = (String) session.getAttribute(getSessionKey());
    String tokenFromRequest = request.getParameter(getTokenName());

    if (tokenFromRequest == null) {
      /** FAIL: token is missing from the request * */
      throw new CsrfGuardException("required token is missing from the request");
    } else if (tokenFromPages != null) {
      if (!tokenFromPages.equals(tokenFromRequest)) {
        /** FAIL: request does not match page token * */
        throw new CsrfGuardException("request token does not match page token");
      }
    } else if (!tokenFromSession.equals(tokenFromRequest)) {
      /** FAIL: the request token does not match the session token * */
      throw new CsrfGuardException("request token does not match session token");
    }
  }
  public static void load(Properties properties)
      throws NoSuchAlgorithmException, InstantiationException, IllegalAccessException,
          ClassNotFoundException, IOException, NoSuchProviderException {
    CsrfGuard csrfGuard = SingletonHolder.instance;

    /** load simple properties * */
    csrfGuard.setLogger(
        (ILogger)
            Class.forName(
                    properties.getProperty(
                        "org.owasp.csrfguard.Logger", "org.owasp.csrfguard.log.ConsoleLogger"))
                .newInstance());
    csrfGuard.setTokenName(
        properties.getProperty("org.owasp.csrfguard.TokenName", "OWASP_CSRFGUARD"));
    csrfGuard.setTokenLength(
        Integer.parseInt(properties.getProperty("org.owasp.csrfguard.TokenLength", "32")));
    csrfGuard.setRotate(
        Boolean.valueOf(properties.getProperty("org.owasp.csrfguard.Rotate", "false")));
    csrfGuard.setTokenPerPage(
        Boolean.valueOf(properties.getProperty("org.owasp.csrfguard.TokenPerPage", "false")));
    csrfGuard.setTokenPerPagePrecreate(
        Boolean.valueOf(
            properties.getProperty("org.owasp.csrfguard.TokenPerPagePrecreate", "false")));
    csrfGuard.setPrng(
        SecureRandom.getInstance(
            properties.getProperty("org.owasp.csrfguard.PRNG", "SHA1PRNG"),
            properties.getProperty("org.owasp.csrfguard.PRNG.Provider", "SUN")));
    csrfGuard.setNewTokenLandingPage(
        properties.getProperty("org.owasp.csrfguard.NewTokenLandingPage"));

    // default to false if newTokenLandingPage is not set; default to true if set.
    if (csrfGuard.getNewTokenLandingPage() == null) {
      csrfGuard.setUseNewTokenLandingPage(
          Boolean.valueOf(
              properties.getProperty("org.owasp.csrfguard.UseNewTokenLandingPage", "false")));
    } else {
      csrfGuard.setUseNewTokenLandingPage(
          Boolean.valueOf(
              properties.getProperty("org.owasp.csrfguard.UseNewTokenLandingPage", "true")));
    }
    csrfGuard.setSessionKey(
        properties.getProperty("org.owasp.csrfguard.SessionKey", "OWASP_CSRFGUARD_KEY"));
    csrfGuard.setAjax(Boolean.valueOf(properties.getProperty("org.owasp.csrfguard.Ajax", "false")));
    csrfGuard.setProtect(
        Boolean.valueOf(properties.getProperty("org.owasp.csrfguard.Protect", "false")));

    /** first pass: instantiate actions * */
    Map<String, IAction> actionsMap = new HashMap<String, IAction>();

    for (Object obj : properties.keySet()) {
      String key = (String) obj;

      if (key.startsWith(ACTION_PREFIX)) {
        String directive = key.substring(ACTION_PREFIX.length());
        int index = directive.indexOf('.');

        /** action name/class * */
        if (index < 0) {
          String actionClass = properties.getProperty(key);
          IAction action = (IAction) Class.forName(actionClass).newInstance();

          action.setName(directive);
          actionsMap.put(action.getName(), action);
          csrfGuard.getActions().add(action);
        }
      }
    }

    /** second pass: initialize action parameters * */
    for (Object obj : properties.keySet()) {
      String key = (String) obj;

      if (key.startsWith(ACTION_PREFIX)) {
        String directive = key.substring(ACTION_PREFIX.length());
        int index = directive.indexOf('.');

        /** action name/class * */
        if (index >= 0) {
          String actionName = directive.substring(0, index);
          IAction action = actionsMap.get(actionName);

          if (action == null) {
            throw new IOException(
                String.format("action class %s has not yet been specified", actionName));
          }

          String parameterName = directive.substring(index + 1);
          String parameterValue = properties.getProperty(key);

          action.setParameter(parameterName, parameterValue);
        }
      }
    }

    /** ensure at least one action was defined * */
    if (csrfGuard.getActions().size() <= 0) {
      throw new IOException("failure to define at least one action");
    }

    /** initialize protected, unprotected pages * */
    for (Object obj : properties.keySet()) {
      String key = (String) obj;

      if (key.startsWith(PROTECTED_PAGE_PREFIX)) {
        String directive = key.substring(PROTECTED_PAGE_PREFIX.length());
        int index = directive.indexOf('.');

        /** page name/class * */
        if (index < 0) {
          String pageUri = properties.getProperty(key);

          csrfGuard.getProtectedPages().add(Pattern.compile(pageUri));
        }
      }

      if (key.startsWith(UNPROTECTED_PAGE_PREFIX)) {
        String directive = key.substring(UNPROTECTED_PAGE_PREFIX.length());
        int index = directive.indexOf('.');

        /** page name/class * */
        if (index < 0) {
          String pageUri = properties.getProperty(key);

          csrfGuard.getUnprotectedPages().add(Pattern.compile(pageUri));
        }
      }
    }

    /** initialize protected methods * */
    String methodList = properties.getProperty("org.owasp.csrfguard.ProtectedMethods");
    if (methodList != null && methodList.trim().length() != 0) {
      for (String method : methodList.split(",")) {
        csrfGuard.getProtectedMethods().add(method.trim());
      }
    }
  }