auth.js

module.exports = function (config, app, passport, DiscordS) {

    const scopes = [
        'identify',
        'guilds'
    ];

    passport.serializeUser((user, done) => {
        done(null, user);
});

    passport.deserializeUser((obj, done) => {
        done(null, obj);
});

    passport.use(new DiscordS({
            clientID: config.clientID,
            clientSecret: config.clientSecret,
            callbackURL: `${config.host}/login/callback`,
            scopes: scopes

        }, (accessToken, refreshToken, profile, done) => {
            process.nextTick(() => {
            return done(null, profile);
});
}));

    app.use(passport.initialize());
    app.use(passport.session());

    app.get("/login", (req, res, next) => {
        if (req.query.redirection) req.session.redirect = req.query.redirection;
    passport.authenticate("discord", {scope: scopes, callbackURL: `${config.host}/login/callback`})(req, res, next);
});

    app.get("/login/callback", passport.authenticate("discord", {failureRedirect: '/error'}), (req, res) => {
        console.log(`- ${req.user.username} has logged on.`);
    if (req.session.redirect === undefined) {
        res.render('error', {
            discord_server: config.discord_server_name,
            config: config,
            loggedInStatus: req.isAuthenticated(),
            userRequest: req.user,
            error_code: "801",
            error_text: `A redirection error has occurred; your session did not store a required redirection URL, and your oauth request could not fully be completed. You are logged in, please <a href='/'>return to the home page.</a>`
        });
        return;
    }
    if (req.session.redirect === `/favicon-32x32.png`) {
        res.redirect("/");
        return;
    }
    res.redirect(req.session.redirect);
});

    app.get("/info", checkAuth, (req, res) => {
        res.json(req.user);
});

    app.get("/logout", (req, res) => {
        req.logout();
    res.redirect("/");
})
};

function checkAuth(req, res, next) {
    if (req.isAuthenticated()) return next();
    res.json('Sorry it appears you arnt logged in!');
}