```
The UI stays minimal and functional. No clutter, just what you need.
![](https://cdn.hashnode.com/res/hashnode/image/upload/v1763703666265/614f93ca-ef32-47ed-9db4-60647e00b36f.png align="center")
### Part 4: The Backend Verifier
The extension needs a backend to verify Self proofs. I built a simple Express server:
```javascript
// server/index.mjs.
import express from 'express';
import { SelfBackendVerifier, AllIds } from '@selfxyz/core';
const app = express();
app.use(express.json());
const selfBackendVerifier = new SelfBackendVerifier(
"demo-scope",
"https://your-ngrok-url.ngrok.io/api/verify",
true, // mockPassport for staging.
AllIds,
{
minimumAge: 18,
excludedCountries: [],
ofac: true
},
"hex"
);
let lastVerificationResult = null;
app.post('/api/verify', async (req, res) => {
const { attestationId, proof, publicSignals, userContextData } = req.body;
try {
const result = await selfBackendVerifier.verifyCredentials(
attestationId,
proof,
publicSignals,
userContextData
);
lastVerificationResult = result;
const { isValid, isMinimumAgeValid, isOfacValid } = result.isValidDetails;
if (!isValid || !isMinimumAgeValid || isOfacValid) {
return res.status(200).json({
status: 'error',
result: false,
reason: !isValid ? 'Invalid proof' :
!isMinimumAgeValid ? 'Under 18' :
'OFAC sanctions list'
});
}
res.json({ status: 'success', result: true });
} catch (error) {
res.status(500).json({ status: 'error', message: error.message });
}
});
app.get('/debug/last-result', (req, res) => {
res.json(lastVerificationResult);
});
app.listen(3001, () => console.log('Server running on port 3001'));
```
**Important**: