public boolean authenticate(Request request,
    Response response,
    LoginConfig config) throws IOException 
{
        // References to objects we will need later
        Session session = null;
        // Have we already authenticated someone?
        Principal principal = request.getUserPrincipal();
        String ssoId = (String) request.getNote(Constants.REQ_SSOID_NOTE);
        if (principal != null) {
            if (log.isDebugEnabled())
                log.debug("Already authenticated '" +
                    principal.getName() + "'");
            // Associate the session with any existing SSO session
            if (ssoId != null)
                associate(ssoId, request.getSessionInternal(true));
            return (true);
        }
        // Is there an SSO session against which we can try to reauthenticate?
        if (ssoId != null) {
            if (log.isDebugEnabled())
                log.debug("SSO Id " + ssoId + " set; attempting " +
                          "reauthentication");
            // Try to reauthenticate using data cached by SSO.  If this fails,
            // either the original SSO logon was of DIGEST or SSL (which
            // we can't reauthenticate ourselves because there is no
            // cached username and password), or the realm denied
            // the user's reauthentication for some reason.
            // In either case we have to prompt the user for a logon */
            if (reauthenticateFromSSO(ssoId, request))
                return true;
        }
        // Have we authenticated this user before but have caching disabled?
        if (!cache) {
            session = request.getSessionInternal(true);
            if (log.isDebugEnabled())
                log.debug("Checking for reauthenticate in session " + session);
            String username =
                (String) session.getNote(Constants.SESS_USERNAME_NOTE);
            String password =
                (String) session.getNote(Constants.SESS_PASSWORD_NOTE);
            if ((username != null) && (password != null)) {
                if (log.isDebugEnabled())
                    log.debug("Reauthenticating username '" + username + "'");
                principal =
                    context.getRealm().authenticate(username, password);
                if (principal != null) {
                    session.setNote(Constants.FORM_PRINCIPAL_NOTE, principal);
                    if (!matchRequest(request)) {
                        register(request, response, principal,
                                 Constants.FORM_METHOD,
                                 username, password);
                        return (true);
                    }
                }
                if (log.isDebugEnabled())
                    log.debug("Reauthentication failed, proceed normally");
            }
        }
        // Is this the re-submit of the original request URI after successful
        // authentication?  If so, forward the *original* request instead.
        if (matchRequest(request)) {
            session = request.getSessionInternal(true);
            if (log.isDebugEnabled())
                log.debug("Restore request from session '"
                          + session.getIdInternal() 
                          + "'");
            principal = (Principal)
                session.getNote(Constants.FORM_PRINCIPAL_NOTE);
            register(request, response, principal, Constants.FORM_METHOD,
                     (String) session.getNote(Constants.SESS_USERNAME_NOTE),
                     (String) session.getNote(Constants.SESS_PASSWORD_NOTE));
            // If we're caching principals we no longer need the username
            // and password in the session, so remove them
            if (cache) {
                session.removeNote(Constants.SESS_USERNAME_NOTE);
                session.removeNote(Constants.SESS_PASSWORD_NOTE);
            }
            if (restoreRequest(request, session)) {
                if (log.isDebugEnabled())
                    log.debug("Proceed to restored request");
                return (true);
            } else {
                if (log.isDebugEnabled())
                    log.debug("Restore of original request failed");
                response.sendError(HttpServletResponse.SC_BAD_REQUEST);
                return (false);
            }
        }
        // Acquire references to objects we will need to evaluate
        MessageBytes uriMB = MessageBytes.newInstance();
        CharChunk uriCC = uriMB.getCharChunk();
        uriCC.setLimit(-1);
        String contextPath = request.getContextPath();
        String requestURI = request.getDecodedRequestURI();
        response.setContext(request.getContext());
        // Is this the action request from the login page?
        boolean loginAction =
            requestURI.startsWith(contextPath) &&
            requestURI.endsWith(Constants.FORM_ACTION);
        // No -- Save this request and redirect to the form login page
        if (!loginAction) {
            session = request.getSessionInternal(true);
            if (log.isDebugEnabled())
                log.debug("Save request in session '" + session.getIdInternal() + "'");
            try {
                saveRequest(request, session);
            } catch (IOException ioe) {
                log.debug("Request body too big to save during authentication");
                response.sendError(HttpServletResponse.SC_FORBIDDEN,
                        sm.getString("authenticator.requestBodyTooBig"));
                return (false);
            }
            forwardToLoginPage(request, response, config);
            return (false);
        }
        // Yes -- Validate the specified credentials and redirect
        // to the error page if they are not correct
        Realm realm = context.getRealm();
        if (characterEncoding != null) {
            request.setCharacterEncoding(characterEncoding);
        }
        String username = request.getParameter(Constants.FORM_USERNAME);
        String password = request.getParameter(Constants.FORM_PASSWORD);
        if (log.isDebugEnabled())
            log.debug("Authenticating username '" + username + "'");
        principal = realm.authenticate(username, password);
        if (principal == null) {
            forwardToErrorPage(request, response, config);
            return (false);
        }
        if (log.isDebugEnabled())
            log.debug("Authentication of '" + username + "' was successful");
        if (session == null)
            session = request.getSessionInternal(false);
        if (session == null) {
            if (containerLog.isDebugEnabled())
                containerLog.debug
                    ("User took so long to log on the session expired");
            response.sendError(HttpServletResponse.SC_REQUEST_TIMEOUT,
                               sm.getString("authenticator.sessionExpired"));
            return (false);
        }
        // Save the authenticated Principal in our session
        session.setNote(Constants.FORM_PRINCIPAL_NOTE, principal);
        // Save the username and password as well
        session.setNote(Constants.SESS_USERNAME_NOTE, username);
        session.setNote(Constants.SESS_PASSWORD_NOTE, password);
        // Redirect the user to the original request URI (which will cause
        // the original request to be restored)
        requestURI = savedRequestURL(session);
        if (log.isDebugEnabled())
            log.debug("Redirecting to original '" + requestURI + "'");
        if (requestURI == null)
            response.sendError(HttpServletResponse.SC_BAD_REQUEST,
                               sm.getString("authenticator.formlogin"));
        else
            response.sendRedirect(response.encodeRedirectURL(requestURI));
        return (false);
}

Authenticate the user making this request, based on the specified login configuration. Return true if any specified constraint has been satisfied, or false if we have created a response challenge already.

 protected  void forwardToErrorPage(Request request,
    Response response,
    LoginConfig config) 
{
        RequestDispatcher disp =
            context.getServletContext().getRequestDispatcher
            (config.getErrorPage());
        try {
            disp.forward(request.getRequest(), response.getResponse());
        } catch (Throwable t) {
            log.warn("Unexpected error forwarding to error page", t);
        }
}

Called to forward to the error page

 protected  void forwardToLoginPage(Request request,
    Response response,
    LoginConfig config) 
{
        RequestDispatcher disp =
            context.getServletContext().getRequestDispatcher
            (config.getLoginPage());
        try {
            disp.forward(request.getRequest(), response.getResponse());
            response.finishResponse();
        } catch (Throwable t) {
            log.warn("Unexpected error forwarding to login page", t);
        }
}

Called to forward to the login page

 public String getCharacterEncoding() 
{
        return characterEncoding;
}

Return the character encoding to use to read the username and password.

 public String getInfo() 
{
    // ------------------------------------------------------------- Properties
        return (info);
}

Return descriptive information about this Valve implementation.

 protected boolean matchRequest(Request request) 
{
      // Has a session been created?
      Session session = request.getSessionInternal(false);
      if (session == null)
          return (false);
      // Is there a saved request?
      SavedRequest sreq = (SavedRequest)
          session.getNote(Constants.FORM_REQUEST_NOTE);
      if (sreq == null)
          return (false);
      // Is there a saved principal?
      if (session.getNote(Constants.FORM_PRINCIPAL_NOTE) == null)
          return (false);
      // Does the request URI match?
      String requestURI = request.getRequestURI();
      if (requestURI == null)
          return (false);
      return (requestURI.equals(sreq.getRequestURI()));
}

Does this request match the saved one (so that it must be the redirect we signalled after successful authentication?

 protected boolean restoreRequest(Request request,
    Session session) throws IOException 
{
        // Retrieve and remove the SavedRequest object from our session
        SavedRequest saved = (SavedRequest)
            session.getNote(Constants.FORM_REQUEST_NOTE);
        session.removeNote(Constants.FORM_REQUEST_NOTE);
        session.removeNote(Constants.FORM_PRINCIPAL_NOTE);
        if (saved == null)
            return (false);
        // Modify our current request to reflect the original one
        request.clearCookies();
        Iterator cookies = saved.getCookies();
        while (cookies.hasNext()) {
            request.addCookie((Cookie) cookies.next());
        }
        MimeHeaders rmh = request.getCoyoteRequest().getMimeHeaders();
        rmh.recycle();
        boolean cachable = "GET".equalsIgnoreCase(saved.getMethod()) ||
                           "HEAD".equalsIgnoreCase(saved.getMethod());
        Iterator names = saved.getHeaderNames();
        while (names.hasNext()) {
            String name = (String) names.next();
            // The browser isn't expecting this conditional response now.
            // Assuming that it can quietly recover from an unexpected 412.
            // BZ 43687
            if(!("If-Modified-Since".equalsIgnoreCase(name) ||
                 (cachable && "If-None-Match".equalsIgnoreCase(name)))) {
                Iterator values = saved.getHeaderValues(name);
                while (values.hasNext()) {
                    rmh.addValue(name).setString( (String)values.next() );
                }
            }
        }
        request.clearLocales();
        Iterator locales = saved.getLocales();
        while (locales.hasNext()) {
            request.addLocale((Locale) locales.next());
        }
        request.getCoyoteRequest().getParameters().recycle();
        if ("POST".equalsIgnoreCase(saved.getMethod())) {
            ByteChunk body = saved.getBody();
            if (body != null) {
                request.getCoyoteRequest().action
                    (ActionCode.ACTION_REQ_SET_BODY_REPLAY, body);
                // Set content type
                MessageBytes contentType = MessageBytes.newInstance();
                //If no content type specified, use default for POST
                String savedContentType = saved.getContentType();
                if (savedContentType == null) {
                    savedContentType = "application/x-www-form-urlencoded";
                }
                contentType.setString(savedContentType);
                request.getCoyoteRequest().setContentType(contentType);
            }
        }
        request.getCoyoteRequest().method().setString(saved.getMethod());
        request.getCoyoteRequest().queryString().setString
            (saved.getQueryString());
        request.getCoyoteRequest().requestURI().setString
            (saved.getRequestURI());
        return (true);
}

Restore the original request from information stored in our session. If the original request is no longer present (because the session timed out), return false; otherwise, return true.

 protected  void saveRequest(Request request,
    Session session) throws IOException 
{
        // Create and populate a SavedRequest object for this request
        SavedRequest saved = new SavedRequest();
        Cookie cookies[] = request.getCookies();
        if (cookies != null) {
            for (int i = 0; i <  cookies.length; i++)
                saved.addCookie(cookies[i]);
        }
        Enumeration names = request.getHeaderNames();
        while (names.hasMoreElements()) {
            String name = (String) names.nextElement();
            Enumeration values = request.getHeaders(name);
            while (values.hasMoreElements()) {
                String value = (String) values.nextElement();
                saved.addHeader(name, value);
            }
        }
        Enumeration locales = request.getLocales();
        while (locales.hasMoreElements()) {
            Locale locale = (Locale) locales.nextElement();
            saved.addLocale(locale);
        }
        if ("POST".equalsIgnoreCase(request.getMethod())) {
            ByteChunk body = new ByteChunk();
            body.setLimit(request.getConnector().getMaxSavePostSize());
            byte[] buffer = new byte[4096];
            int bytesRead;
            InputStream is = request.getInputStream();
            while ( (bytesRead = is.read(buffer) )  >= 0) {
                body.append(buffer, 0, bytesRead);
            }
            saved.setContentType(request.getContentType());
            saved.setBody(body);
        }
        saved.setMethod(request.getMethod());
        saved.setQueryString(request.getQueryString());
        saved.setRequestURI(request.getRequestURI());
        // Stash the SavedRequest in our session for later use
        session.setNote(Constants.FORM_REQUEST_NOTE, saved);
}

Save the original request information into our session.

 protected String savedRequestURL(Session session) 
{
        SavedRequest saved =
            (SavedRequest) session.getNote(Constants.FORM_REQUEST_NOTE);
        if (saved == null)
            return (null);
        StringBuffer sb = new StringBuffer(saved.getRequestURI());
        if (saved.getQueryString() != null) {
            sb.append('?");
            sb.append(saved.getQueryString());
        }
        return (sb.toString());
}

Return the request URI (with the corresponding query string, if any) from the saved request so that we can redirect to it.

 public  void setCharacterEncoding(String encoding) 
{
        characterEncoding = encoding;
}

Set the character encoding to be used to read the username and password.