Implementing Slack Oauth 2.0 for www.workat.com

callback.js

const loginCallback = async (req, res, next) => {
  const redirectUri = 'https://...'; // would be the URL defined above
  const slackClient = await getSlackOpenIdClient(redirectUri);
  const { slackLoginVerifyCode } = req.session;
  const tokenSet = await slackClient.callback(
    redirectUri,
    req.query,
    { code_verifier: slackLoginVerifyCode }
  );
  const { access_token: accessToken } = tokenSet;
  const {
    'https://slack.com/team_id': teamId,
    'https://slack.com/target_uri': targetUri,
    'https://slack.com/user_id': slackUserId
  } = tokenSet.claims();
};

  

login.js

'use strict';

const { Issuer, generators } = require('openid-client');
const {
  slackClientId,
  slackClientSecret,
  slackOpenIdIssuer
} = require('./config'); // your own configs

// Keep in memory to reduce calls
let issuer;

const getSlackOpenIdClient = async (callbackUri) => {
  if (!issuer) {
    issuer = await Issuer.discover(slackOpenIdIssuer);
  }
  return new issuer.Client({
    client_id: slackClientId,
    client_secret: slackClientSecret,
    redirect_uris: [callbackUri],
  });
};

const login = async (req, res, next) => {
  const { state } = req.query;
  try {
    // eslint-disable-next-line max-len
    const callbackUri = 'https://..../callback'; // where slack will send the user back after authorization
    const slackClient = await getSlackOpenIdClient(callbackUri);
    
    // Generate code and save in session
    const codeVerifier = generators.codeVerifier();
    req.session.slackLoginVerifyCode = codeVerifier;

    const codeChallenge = generators.codeChallenge(codeVerifier);
    const slackLoginUrl = slackClient.authorizationUrl({
      scope: LOGIN_SCOPES,
      code_challenge: codeChallenge,
      code_challenge_method: 'S256',
    });
    return res.redirect(slackLoginUrl);
  } catch (err) {
    logger.error('Error during slack login', err);
    return next(err);
  }
};