Quick fix for OAuth2 OOB deprecation - provide explicit callback and respond to user with token

* see greghesp#272)
* see https://developers.google.com/identity/protocols/oauth2/resources/oob-migration
* IMPORTANT: Make sure your credentials have the property `"redirect_uris":["http://your-relay-server-hostname:your-relay-server-port/auth/callback"]}`

Author: mcmoe

relay/routes/index.js

@@ -12,10 +12,14 @@ const router = express.Router();
 
 
 router.get('/', function(req, res) {
-  console.log("Get All")
+  console.log("Get All");
   res.sendFile(path.join(__dirname, '../views', 'index.html'));
  });
 
+router.get('/auth/callback', function(req, res) {
+  res.status(200).json(req.query);
+ });
+
 router.post('/assistant', async(req, res) => {
   try {
     const db = await low(adapter);