React implicit grant JWT validation failing on exp claim

Building a React app using the implicit grant flow for Genesys Cloud auth. The @genesyscloud/purecloud-platform-auth library handles the token exchange, but my custom JWT validation middleware keeps rejecting the access token immediately after refresh.

The exp claim in the decoded token is always in the past, even though the token was just issued. Here’s the validation logic I’m using:

const jwt = require('jsonwebtoken');

const validateToken = (token) => {
 try {
 const decoded = jwt.decode(token, { complete: true });
 if (!decoded) throw new Error('Invalid token');
 
 const now = Math.floor(Date.now() / 1000);
 console.log('Token exp:', decoded.payload.exp);
 console.log('Current time:', now);
 
 if (decoded.payload.exp < now) {
 throw new Error('Token expired');
 }
 return decoded.payload;
 } catch (err) {
 console.error('JWT Validation Error:', err.message);
 return null;
 }
};

The console output shows Token exp is exactly 1 second less than Current time. Is there a clock skew issue with Genesys Cloud’s token signing, or am I missing a step in the implicit grant flow?

You’re likely comparing UTC timestamps against a local clock without normalizing. The exp claim is always seconds since epoch in UTC. If your middleware runs in a timezone-aware environment or uses Date.now() incorrectly, the math breaks.

Here’s the fix. Use jwt.verify with the correct clock tolerance or handle the comparison manually.

const jwt = require('jsonwebtoken');

// Option 1: Let jwt library handle it (recommended)
try {
 const decoded = jwt.verify(token, publicKey, { algorithms: ['RS256'], clockTolerance: 60 });
 console.log('Token valid:', decoded);
} catch (err) {
 console.error('Validation failed:', err.message);
}

// Option 2: Manual check if you're doing custom validation
const now = Math.floor(Date.now() / 1000);
if (decoded.exp <= now) {
 throw new Error('Token expired');
}

The clockTolerance option adds a buffer (in seconds) to account for clock drift between the auth server and your app. Genesys tokens usually expire in 1 hour, but network latency or server time skew can cause immediate failures if you’re strict.

Also, ensure you’re using the correct public key from the JWKS endpoint. Implicit grant doesn’t give you a refresh token, so if the access token expires, you’re stuck. You’ll need to re-authenticate the user. Don’t try to extend the session manually; it’s a security risk.

Check your server’s NTP sync. If your server time is off by even a minute, you’ll see this issue. Run date on your server and compare with api.genesys.cloud time. If they differ, fix the clock.

One more thing: make sure you’re not accidentally decoding the token twice. Some libraries return a pre-decoded object, others return the raw string. If you’re passing a string to jwt.verify, it works. If you pass an object, it fails. Check your input type.

This should resolve the immediate validation failure. If it persists, dump the raw token header and payload to verify the exp value matches expectations.