@Override
  protected ModelAndView handleRequestInternal(
      final HttpServletRequest request, final HttpServletResponse response) throws Exception {
    // get CAS ticket
    final String ticket = request.getParameter(OAuthConstants.TICKET);
    log.debug("ticket : {}", ticket);

    ServiceTicket serviceTicket = (ServiceTicket) ticketRegistry.getTicket(ticket);
    TicketGrantingTicket grantingTicket = serviceTicket.getGrantingTicket();
    log.debug("granting ticket : {}", grantingTicket);
    if (grantingTicket == null) return null;

    // retrieve callback url from session
    final HttpSession session = request.getSession();
    String callbackUrl = (String) session.getAttribute(OAuthConstants.OAUTH20_CALLBACKURL);
    log.debug("callbackUrl : {}", callbackUrl);
    session.removeAttribute(OAuthConstants.OAUTH20_CALLBACKURL);
    // and state
    final String state = (String) session.getAttribute(OAuthConstants.OAUTH20_STATE);
    log.debug("state : {}", state);
    session.removeAttribute(OAuthConstants.OAUTH20_STATE);

    if (callbackUrl == null) return null;

    // return callback url with code & state
    callbackUrl = OAuthUtils.addParameter(callbackUrl, OAuthConstants.CODE, ticket);
    if (state != null) {
      callbackUrl = OAuthUtils.addParameter(callbackUrl, OAuthConstants.STATE, state);
    }
    log.debug("callbackUrl : {}", callbackUrl);

    final Map<String, Object> model = new HashMap<String, Object>();
    model.put("callbackUrl", callbackUrl);
    // retrieve service name from session
    final String serviceName = (String) session.getAttribute(OAuthConstants.OAUTH20_SERVICE_NAME);
    log.debug("serviceName : {}", serviceName);
    model.put("serviceName", serviceName);

    model.put("userId", grantingTicket.getAuthentication().getPrincipal().getId());

    return new ModelAndView(OAuthConstants.CONFIRM_VIEW, model);
  }
  @Audit(
      action = "SERVICE_TICKET_VALIDATE",
      actionResolverName = "VALIDATE_SERVICE_TICKET_RESOLVER",
      resourceResolverName = "VALIDATE_SERVICE_TICKET_RESOURCE_RESOLVER")
  @Timed(name = "VALIDATE_SERVICE_TICKET_TIMER")
  @Metered(name = "VALIDATE_SERVICE_TICKET_METER")
  @Counted(name = "VALIDATE_SERVICE_TICKET_COUNTER", monotonic = true)
  @Transactional(readOnly = false)
  @Override
  public Assertion validateServiceTicket(final String serviceTicketId, final Service service)
      throws TicketException {
    final RegisteredService registeredService = this.servicesManager.findServiceBy(service);
    verifyRegisteredServiceProperties(registeredService, service);

    final ServiceTicket serviceTicket =
        this.serviceTicketRegistry.getTicket(serviceTicketId, ServiceTicket.class);

    if (serviceTicket == null) {
      logger.info("Service ticket [{}] does not exist.", serviceTicketId);
      throw new InvalidTicketException(serviceTicketId);
    }

    try {
      synchronized (serviceTicket) {
        if (serviceTicket.isExpired()) {
          logger.info("ServiceTicket [{}] has expired.", serviceTicketId);
          throw new InvalidTicketException(serviceTicketId);
        }

        if (!serviceTicket.isValidFor(service)) {
          logger.error(
              "Service ticket [{}] with service [{}] does not match supplied service [{}]",
              serviceTicketId,
              serviceTicket.getService().getId(),
              service);
          throw new UnrecognizableServiceForServiceTicketValidationException(
              serviceTicket.getService());
        }
      }

      final TicketGrantingTicket root = serviceTicket.getGrantingTicket().getRoot();
      final Authentication authentication =
          getAuthenticationSatisfiedByPolicy(
              root, new ServiceContext(serviceTicket.getService(), registeredService));
      final Principal principal = authentication.getPrincipal();

      final AttributeReleasePolicy attributePolicy = registeredService.getAttributeReleasePolicy();
      logger.debug(
          "Attribute policy [{}] is associated with service [{}]",
          attributePolicy,
          registeredService);

      @SuppressWarnings("unchecked")
      final Map<String, Object> attributesToRelease =
          attributePolicy != null
              ? attributePolicy.getAttributes(principal)
              : Collections.EMPTY_MAP;

      final String principalId =
          registeredService.getUsernameAttributeProvider().resolveUsername(principal, service);
      final Principal modifiedPrincipal =
          this.principalFactory.createPrincipal(principalId, attributesToRelease);
      final AuthenticationBuilder builder = AuthenticationBuilder.newInstance(authentication);
      builder.setPrincipal(modifiedPrincipal);

      return new ImmutableAssertion(
          builder.build(),
          serviceTicket.getGrantingTicket().getChainedAuthentications(),
          serviceTicket.getService(),
          serviceTicket.isFromNewLogin());
    } finally {
      if (serviceTicket.isExpired()) {
        this.serviceTicketRegistry.deleteTicket(serviceTicketId);
      }
    }
  }
  @Audit(
      action = "SERVICE_TICKET",
      actionResolverName = "GRANT_SERVICE_TICKET_RESOLVER",
      resourceResolverName = "GRANT_SERVICE_TICKET_RESOURCE_RESOLVER")
  @Profiled(tag = "GRANT_SERVICE_TICKET", logFailuresSeparately = false)
  @Transactional(readOnly = false)
  @Override
  public String grantServiceTicket(
      final String ticketGrantingTicketId, final Service service, final Credential... credentials)
      throws AuthenticationException, TicketException {
    Assert.notNull(ticketGrantingTicketId, "ticketGrantingticketId cannot be null");
    Assert.notNull(service, "service cannot be null");

    final TicketGrantingTicket ticketGrantingTicket =
        this.ticketRegistry.getTicket(ticketGrantingTicketId, TicketGrantingTicket.class);

    if (ticketGrantingTicket == null) {
      logger.debug(
          "TicketGrantingTicket [{}] cannot be found in the ticket registry.",
          ticketGrantingTicketId);
      throw new InvalidTicketException(ticketGrantingTicketId);
    }

    synchronized (ticketGrantingTicket) {
      if (ticketGrantingTicket.isExpired()) {
        this.ticketRegistry.deleteTicket(ticketGrantingTicketId);
        logger.debug(
            "TicketGrantingTicket[{}] has expired and is now deleted from the ticket registry.",
            ticketGrantingTicketId);
        throw new InvalidTicketException(ticketGrantingTicketId);
      }
    }

    final RegisteredService registeredService = this.servicesManager.findServiceBy(service);

    verifyRegisteredServiceProperties(registeredService, service);

    if (!registeredService.isSsoEnabled()
        && credentials == null
        && ticketGrantingTicket.getCountOfUses() > 0) {
      logger.warn("ServiceManagement: Service [{}] is not allowed to use SSO.", service.getId());
      throw new UnauthorizedSsoServiceException();
    }

    // CAS-1019
    final List<Authentication> authns = ticketGrantingTicket.getChainedAuthentications();
    if (authns.size() > 1) {
      if (!registeredService.isAllowedToProxy()) {
        final String message =
            String.format(
                "ServiceManagement: Proxy attempt by service [%s] (registered service [%s]) is not allowed.",
                service.getId(), registeredService.toString());
        logger.warn(message);
        throw new UnauthorizedProxyingException(message);
      }
    }

    if (credentials != null) {
      final Authentication current = this.authenticationManager.authenticate(credentials);
      final Authentication original = ticketGrantingTicket.getAuthentication();
      if (!current.getPrincipal().equals(original.getPrincipal())) {
        throw new MixedPrincipalException(current, current.getPrincipal(), original.getPrincipal());
      }
      ticketGrantingTicket.getSupplementalAuthentications().add(current);
    }

    // Perform security policy check by getting the authentication that satisfies the configured
    // policy
    // This throws if no suitable policy is found
    getAuthenticationSatisfiedByPolicy(
        ticketGrantingTicket, new ServiceContext(service, registeredService));

    final String uniqueTicketIdGenKey = service.getClass().getName();
    if (!this.uniqueTicketIdGeneratorsForService.containsKey(uniqueTicketIdGenKey)) {
      logger.warn(
          "Cannot create service ticket because the key [{}] for service [{}] is not linked to a ticket id generator",
          uniqueTicketIdGenKey,
          service.getId());
      throw new UnauthorizedSsoServiceException();
    }

    final UniqueTicketIdGenerator serviceTicketUniqueTicketIdGenerator =
        this.uniqueTicketIdGeneratorsForService.get(uniqueTicketIdGenKey);

    final String generatedServiceTicketId =
        serviceTicketUniqueTicketIdGenerator.getNewTicketId(ServiceTicket.PREFIX);
    logger.debug(
        "Generated service ticket id [{}] for ticket granting ticket [{}]",
        generatedServiceTicketId,
        ticketGrantingTicket.getId());

    final ServiceTicket serviceTicket =
        ticketGrantingTicket.grantServiceTicket(
            generatedServiceTicketId,
            service,
            this.serviceTicketExpirationPolicy,
            credentials != null);

    this.serviceTicketRegistry.addTicket(serviceTicket);

    if (logger.isInfoEnabled()) {
      final List<Authentication> authentications =
          serviceTicket.getGrantingTicket().getChainedAuthentications();
      final String formatString = "Granted %s ticket [%s] for service [%s] for user [%s]";
      final String type;
      final String principalId =
          authentications.get(authentications.size() - 1).getPrincipal().getId();

      if (authentications.size() == 1) {
        type = "service";
      } else {
        type = "proxy";
      }

      logger.info(
          String.format(formatString, type, serviceTicket.getId(), service.getId(), principalId));
    }

    return serviceTicket.getId();
  }
  @Override
  protected ModelAndView handleRequestInternal(
      final HttpServletRequest request, final HttpServletResponse response) throws Exception {
    final HttpSession session = request.getSession();

    // get cas login service ticket
    final String serviceTicketId = request.getParameter(OAuthConstants.TICKET);
    LOGGER.debug("{} : {}", OAuthConstants.TICKET, serviceTicketId);

    // first time this url is requested the login ticket will be a query parameter
    if (serviceTicketId != null) {
      // create the login ticket granting ticket
      final ServiceTicket serviceTicket = (ServiceTicket) ticketRegistry.getTicket(serviceTicketId);
      // login service ticket should be valid
      if (serviceTicket == null || serviceTicket.isExpired()) {
        LOGGER.error("Service Ticket expired : {}", serviceTicketId);
        return OAuthUtils.writeTextError(
            response, OAuthConstants.INVALID_GRANT, HttpStatus.SC_BAD_REQUEST);
      }
      final TicketGrantingTicket ticketGrantingTicket = serviceTicket.getGrantingTicket();
      // remove login service ticket
      ticketRegistry.deleteTicket(serviceTicket.getId());

      // store the login tgt id in the user's session, used to create service tickets for validation
      // and
      // oauth credentials later in the flow.
      session.setAttribute(OAuthConstants.OAUTH20_LOGIN_TICKET_ID, ticketGrantingTicket.getId());

      // redirect back to self, clears the service ticket from the url, allows the url to be
      // requested multiple
      // times w/o error
      return OAuthUtils.redirectTo(request.getRequestURL().toString());
    }

    // get cas login service ticket from the session
    String ticketGrantingTicketId =
        (String) session.getAttribute(OAuthConstants.OAUTH20_LOGIN_TICKET_ID);
    LOGGER.debug("{} : {}", OAuthConstants.TICKET, ticketGrantingTicketId);
    if (StringUtils.isBlank(ticketGrantingTicketId)) {
      LOGGER.error("Missing Ticket Granting Ticket");
      return OAuthUtils.writeTextError(
          response, OAuthConstants.INVALID_GRANT, HttpStatus.SC_BAD_REQUEST);
    }

    // verify the login ticket granting ticket is still valid
    TicketGrantingTicket ticketGrantingTicket =
        (TicketGrantingTicket) ticketRegistry.getTicket(ticketGrantingTicketId);
    if (ticketGrantingTicket == null || ticketGrantingTicket.isExpired()) {
      LOGGER.error("Ticket Granting Ticket expired : {}", ticketGrantingTicketId);
      return OAuthUtils.writeTextError(
          response, OAuthConstants.INVALID_GRANT, HttpStatus.SC_BAD_REQUEST);
    }

    String callbackUrl =
        request
            .getRequestURL()
            .toString()
            .replace(
                "/" + OAuthConstants.CALLBACK_AUTHORIZE_URL,
                "/" + OAuthConstants.CALLBACK_AUTHORIZE_ACTION_URL);
    LOGGER.debug("{} : {}", OAuthConstants.CALLBACK_AUTHORIZE_ACTION_URL, callbackUrl);

    String allowCallbackUrl =
        OAuthUtils.addParameter(
            callbackUrl,
            OAuthConstants.OAUTH20_APPROVAL_PROMPT_ACTION,
            OAuthConstants.OAUTH20_APPROVAL_PROMPT_ACTION_ALLOW);

    final Map<String, Object> model = new HashMap<>();
    model.put("callbackUrl", callbackUrl);

    final Boolean bypassApprovalPrompt =
        (Boolean) session.getAttribute(OAuthConstants.BYPASS_APPROVAL_PROMPT);
    LOGGER.debug("bypassApprovalPrompt : {}", bypassApprovalPrompt);
    if (bypassApprovalPrompt != null && bypassApprovalPrompt) {
      return OAuthUtils.redirectTo(allowCallbackUrl);
    }

    final String clientId = (String) session.getAttribute(OAuthConstants.OAUTH20_CLIENT_ID);
    LOGGER.debug("{} : {}", OAuthConstants.CLIENT_ID, clientId);

    final Principal loginPrincipal = ticketGrantingTicket.getAuthentication().getPrincipal();

    final String approvalPrompt =
        (String) session.getAttribute(OAuthConstants.OAUTH20_APPROVAL_PROMPT);
    LOGGER.debug("approvalPrompt : {}", approvalPrompt);
    if (StringUtils.isBlank(approvalPrompt)
        || !approvalPrompt.equalsIgnoreCase(OAuthConstants.APPROVAL_PROMPT_FORCE)) {
      final TicketGrantingTicket refreshToken =
          OAuthTokenUtils.getRefreshToken(centralAuthenticationService, clientId, loginPrincipal);
      if (refreshToken != null) {
        return OAuthUtils.redirectTo(allowCallbackUrl);
      }
    }

    // retrieve service name from session
    final String serviceName = (String) session.getAttribute(OAuthConstants.OAUTH20_SERVICE_NAME);
    LOGGER.debug("serviceName : {}", serviceName);
    model.put("serviceName", serviceName);

    return new ModelAndView(OAuthConstants.CONFIRM_VIEW, model);
  }