Here's a simple gist for getting a user before another route handles the actual command.

api.js

var express = require('express');
var router = express.Router();

router.use(function (req, res, next) {
    User.findOne(1234, function(err, user) {
        if (err) {
            console.log(err);
            res.json({ error: 'There was an error' });
        }
        else {
            res.locals.user = user;
            next();
        }
    });
});

router.get('/get/id', function (req, res) {
    res.json({ id: res.locals.user.id });
});

router.get('/get/name', function (req, res) {
    res.json({ name: res.locals.user.name });
});

app.js

...

app.use('/api/v1', require('./api.js'));

....