Ionic Token authentication php Server - Security questions [duplicate] - php

Question

I have two applications:
server ( REST API Server)
node js
Express
jsonwebtokens
express-jwt
mongoose
client (Portable Front-end)
bootstrap
Angular JS
local-storage
angular-facebook
angular-jwt
Lateron, the client app will be ported for android, iphone and other platforms using phonegap. For OAuth, I am using Facebook as the provider. Now, I just realized JSON Web Tokens are the way to go for this kind of set up. My question is an architectural one rather than syntactical one - how to manage a secret key when signing the facebook access token and user id with JWT in nodejs?
So this is how the flow works in my app:
Angular client has a Login button
User Clicks the button > Facebook Auth starts
Client receives user_id and FB Access Token
Client sends[POST json body] both user_id and Access Token to Node+Express Server at 'http://server.com/auth/login'
Node Server has applied express-jwt to all routes except /auth/login with a
var expressJwt = require('express-jwt');
var jwt = require('jsonwebtoken');
app.use(expressjwt({ secret: ''}).unless({path: ['/auth/login']}));
Node server receives data from req.body, fetches all profile details from facebook using the JavascriptSDK, and signs it using
var token=expressjwt.sign({profile}, );
Node Server stores(updates, if user_id exists) the new token in db and sends it as response to client
client stores the new token it received as json data in local-storage
client uses angular-jwt to fetch profile data from the new token and automatically attach the new token in Authorization header for all requests it sends to the server
Now, my questions are:
Do I really need to store the JWT tokens in database? I am certainly not comparing the tokens in request headers with database
Do I need to generate random secret keys for security, each time a person logs in? If yes then how would that fit in both client and server?
When and where do I need to check for token expiration? and How do I refresh it?
I am kind of lost about the design flow and mechanism.

Answer 1

Ad 1. You do not have to store the JWT in the database. User ID can be part of the payload, therefore there's no need for it.
Ad 2. It's a common practice for the server side app to use one secret key for generating all JWT.
Ad 3. Check if token has expired on each request to your API and disallow access if the token has expired, return 401 status code. Client app should prompt user for credentials and request new JWT. If you want to avoid users re-submitting the credentials you can issue a refresh token that later can be used to generate new JWT.
JWT refresh token flow
http://bitoftech.net/2014/07/16/enable-oauth-refresh-tokens-angularjs-app-using-asp-net-web-api-2-owin/