// jwt_server.js - Vulnerable JWT verification server
const express = require('express');
const jwt = require('jsonwebtoken');
const jwksClient = require('jwks-rsa');
const axios = require('axios');

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

// Normally fetches public key from a JWKS endpoint, but vulnerable kid handling
async function getPublicKey(kid) {
    // Attacker can inject a kid that points to their own URL
    if (kid.startsWith('http://') || kid.startsWith('https://')) {
        // Fetch the key from attacker-controlled URL (INSECURE!)
        const response = await axios.get(kid);
        return response.data.publicKey; // expects PEM
    }
    // Otherwise use local JWKS (simulated)
    return `-----BEGIN PUBLIC KEY-----
MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAu1SU1LfVLPHCYZM5rPY4
...
-----END PUBLIC KEY-----`;
}

app.post('/api/verify', async (req, res) => {
    const token = req.body.token;
    const decoded = jwt.decode(token, { complete: true });
    const kid = decoded.header.kid;
    try {
        const publicKey = await getPublicKey(kid);
        const payload = jwt.verify(token, publicKey, { algorithms: ['RS256','HS256'] });
        res.json({ status: 'authenticated', user: payload.sub });
    } catch (e) {
        res.status(401).json({ error: e.message });
    }
});

app.listen(3000, () => console.log('JWT server on :3000'));