how to do i get user id from JWT token? [duplicate] - node.js

Question

I tried to get user id from a JWT token. I got a JWT token and sucessfully verified it, but it doesn't return an id.
When I decode the JWT:
const decoded = jwt.verify(token, config.get('jwtPrivateKey'));
var userId = decoded.id
console.log(decoded)
I got this output:
{ iat: 1561463667 }
But I excepted this output:
id :"*****************"
How do I get the user id from the token?

Answer 1

When the whole output is { iat: 1561463667 }, it means, that no extra payload/claims were added when the token was signed.
The jsonwebtoken package usually adds iat (issuedAt, the time when the token was issued) as a default claim.
In simple words: you can only decode claims, that were added before.
To add more claims, try this code (when you're in control of the code which issues the token):
let payload = { "id" : "1"};
let token = jwt.sign( payload,'secret', { noTimestamp:true, expiresIn: '1h' });
Here I added an expiry time (exp), and set the option noTimestamp to suppress the automatically added iat claim.
The result looks like this:
{
"id": "1",
"exp": 1561471747
}
and the token:
eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpZCI6IjEiLCJleHAiOjE1NjE0NzI0MzV9.jmKyITRoxLl0fy0-rrwgPOA_iRgGQu8W4Cc6dPupOMA
Then you can get the id as you have already shown in your question:
const decoded = jwt.verify(token, "your secret or key");
var userId = decoded.id
console.log(userId)
You can also paste the above shown JWT or your token into the https://jwt.io debugger, to inspect the token and see the structure and the actual claim names. Maybe there's no id, but a userId or similar, or a subclaim, which is a registerd claim name to be used to identify the principal:
The "sub" (subject) claim identifies the principal that is the
subject of the JWT.
It might also happen, that the token contains nested objects, e.g.:
{
"user_data":
{
"user_id": "1",
"user_name: "superuser"
},
"exp": 1561471747
}
then you get the user_id this way:
const decoded = jwt.verify(token, "your secret or key");
var userId = decoded.user_data.user_id
console.log(userId)