Consolidated API keys with express gateway

gateway.js

const Keen = require('keen-js');
const Mailgun = require('mailgun-js');
const bodyParser = require('body-parser');
const express = require('express');

const app = express();
app.use(bodyParser.json());

const keys = {
  // Top-level is the gateway's API keys, so user will send `token-1` to the
  // gateway and get access to the underlying API keys without knowing what they
  // are.
  'token-1': {
    keen: {
      // Keys hidden so malicious users don't max out my KeenIO free tier :)
      projectId: '...',
      writeKey: '...'
    },
    mailgun: {
      apiKey: '...',
      domain: '...'
    }
  },
  'token-2': {
    keen: {
      projectId: '...',
      writeKey: '...'
    },
    mailgun: {
      apiKey: '...',
      domain: '...'
    }
  }
};

app.use(wrap(async function(req, res, next) {
  if (!req.headers['authorization']) {
    throw new Error('Must have auth header!');
  }
  if (!keys[req.headers['authorization']]) {
    throw new Error(`Invalid auth token ${req.headers['authorization']}`);
  }
}));

app.use('/keen', keen());
app.use('/mailgun', mailgun());

app.listen(3000);

function keen() {
  const router = express.Router();

  router.use(wrap(async function(req, res, next) {
    req.client = new Keen(keys[req.headers['authorization']].keen);
  }));

  router.post('/track/:event', wrap(async function(req, res) {
    await req.client.addEvent(req.params.event, req.body);
    return { ok: 1 };
  }));

  return router;
}

function mailgun() {
  const router = express.Router();

  router.use(wrap(async function(req, res, next) {
    req.client = new Mailgun(keys[req.headers['authorization']].mailgun);
  }));

  router.post('/send', wrap(async function(req, res) {
    await req.client.messages().send(req.body);
    return { ok: 1 };
  }));

  return router;
}

function wrap(fn) {
  return function(req, res, next) {
    // Make sure to `.catch()` any errors and pass them along to the `next()`
    // middleware in the chain, in this case the error handler.
    fn(req).
      then(returnVal => {
        if (returnVal != null) {
          return res.send(returnVal);
        }
        return next();
      }).
      catch(next);
  };
}