app.get(
    '/auth/trello_provider/callback',
    passport.authenticate('trello', { failureRedirect: '/unauth' }),
    (req, res) => res.redirect('/')
);

const ensureAuthenticatedForApiRequests = (req, res, next) => {
    if (req.isAuthenticated()) {
        return next();
    }

    return res.status(401).json({
        status:     'Unauthorized',
        statusCode: 401,
        message:    'You are not authorized. Go away!',
    });
};

app.get(
    '/api/contact/:contactId',
    ensureAuthenticatedForApiRequests,
    (req, res) => {
        // ...
    }
);

app.get('/route', passport.authenticate(['strategy1', 'strategy2'], (req, res) => {
    // ...
});