OIDC Back-Channel Logout

const express = require('express');
const router = express.Router();
const { requiresAuth } = require('express-openid-connect');

// middleware to validate the logout token
const requiresValidLogoutToken = require('../middlewares/validateLogoutToken');

// helper function to delete user sessions
const deleteUserSessions = require('../utils/sessions');

// new route to receive backchannel logout tokens
// must be configured in the Application -> Sessions tab 
// in the Auth0 Management Dashboard
router.post(
  '/backchannel-logout',
  requiresValidLogoutToken,
  function (req, res, next) {
    // at this point the logout token is valid, checked by requiresValidLogoutToken middleware
    // you can access it from the request object: req.logoutToken

    // delete user session so the user gets logged out
    deleteUserSessions(
      req.app.locals.sessionStore,
      req.logoutToken.sub,
      req.logoutToken.sid
    );

    res.sendStatus(200);
  }
);

router.get('/', function (req, res, next) {
  res.render('index', {
    title: 'Auth0 Webapp sample Nodejs',
    isAuthenticated: req.oidc.isAuthenticated(),
    headline: process.env.APP_NAME,
    backgroundColor: process.env.BACKGROUND_COLOR,
    baseURL: process.env.BASE_URL,
  });
});

router.get('/profile', requiresAuth(), function (req, res, next) {
  res.render('profile', {
    userProfile: JSON.stringify(req.oidc.user, null, 2),
    title: 'Profile page',
    headline: process.env.APP_NAME,
    backgroundColor: process.env.BACKGROUND_COLOR,
    baseURL: process.env.BASE_URL,
  });
});

module.exports = router;

// This middleware validates the logout token as defined here:
// https://openid.net/specs/openid-connect-backchannel-1_0.html#Validation

const jose = require('jose');

async function requiresValidLogoutToken(req, res, next) {

  // get remote key set for token verification
  const JWKS = jose.createRemoteJWKSet(
    new URL(process.env.ISSUER_BASE_URL + '/.well-known/jwks.json')
  );

  const logoutToken = req.body.logout_token;

  if (!logoutToken) {
    res.status(400).send('Need logout token');
  }

  try {
    const { payload, protectedHeader } = await jose.jwtVerify(
      logoutToken,
      JWKS,
      {
        issuer: process.env.ISSUER_BASE_URL + '/',
        audience: process.env.CLIENT_ID,
        typ: 'JWT',
        maxTokenAge: '2 minutes',
      }
    );

    // Verify that the Logout token contains a sub claim, a sid claim, or both
    if (!payload.sub && !payload.sid) {
      res
        .status(400)
        .send(
          'Error: Logout token must contain either sub claim or sid claim, or both'
        );
    }

    // Verify that the logout token contains an events claim
    // whose value is a JSON object containing the member name http://schemas.openid.net/event/backchannel-logout
    if (!payload.events['http://schemas.openid.net/event/backchannel-logout']) {
      res
        .status(400)
        .send(
          'Error: Logout token must contain events claim with correct schema'
        );
    }

    // Verify that the Logout token does not contain a nonce claim.
    if (payload.nonce) {
      res
        .status(400)
        .send('Error: Logout token must not contain a nonce claim');
    }

    // attach valid logout token to request object
    req.logoutToken = payload;

    // token is valid, call next middleware
    next();
  } catch (error) {
    res.status(400).send(`Error:  ${error.message}`);
  }
}

module.exports = requiresValidLogoutToken;