Backend redirect

.env.dev

#CANONICAL-URL
FRONT_END_URL=http://localhost:3000
DOMAIN=localhost

...
#OTHER STUFF

auth.js

const conf = require('../../config/config');

// auth routers
router.get('/:provider', (req, res, next) => {
    passport.authenticate(provider, options)(req, res, next);
});

// callbacks
router.get('/:provider/callback', (req, res, next) => {
    passport.authenticate(req.params.provider, function (err, user, info) {
            // YOUR CODE
        
        req.logIn(user, { session: false }, function (err) {
            if (err) {
                // DO ERROR
            }
            const token = signToken(user);

            return res
                .status(200)
                .cookie('jwt', token, { httpOnly: true, domain: conf.DOMAIN })
                .redirect(redirectUponLogin(state.referer, flowId));
        });
    })(req, res, next);
});

config.js

const dotenv = require('dotenv');

if (process.env.NODE_ENV === 'production') {
    dotenv.config({ path: '../.env' });
} else {
    dotenv.config({ path: '../.env.dev' });
}

passport-setup.js

const generateCallbackURL = (provider) => {
    return `${conf.FRONT_END_URL}/api/auth/${provider}/callback`
}

// Google Strategy
passport.use(
    new GoogleStrategy(
        {
            clientID: credentials.GOOGLE.client_id,
            clientSecret: credentials.GOOGLE.client_secret,
            callbackURL: generateCallbackURL('google'),
            passReqToCallback: true,
        },
        (req, accessToken, refreshToken, profile, done) => {
            const email = profile.emails.filter((email) => email.verified)[0].value
            findByEmailOrCreate(email, req, profile, done)
        }
    )
)

// Facebook Strategy
passport.use(
    new FacebookStrategy(
        {
            clientID: credentials.FACEBOOK.client_id,
            clientSecret: credentials.FACEBOOK.client_secret,
            callbackURL: generateCallbackURL('facebook'),
            passReqToCallback: true,
            profileFields: [
                'id',
                'email',
                'gender',
                'link',
                'locale',
                'name',
                'displayName',
                'timezone',
                'updated_time',
                'verified',
            ],
        },
        function (req, accessToken, refreshToken, profile, done) {
            const email = profile.emails[0].value
            findByEmailOrCreate(email, req, profile, done)
        }
    )
)

//Other strategies