NodejsMetamaskNftAuthentication route

// Process signed message
router.post('/:user/signature', (req, res) => {
    // Get user from db
    db.get('SELECT * FROM users WHERE address = ?', [req.params.user], (err, row) => {
        if (err) {
            console.error(err.message);
            return res.status(500).send(err.message);
        }
        if (row) {
            const msg = `Nonce: ${row.nonce}`;
            console.log("User nonce from db: " + row.nonce);
            // Convert msg to hex string
            const msgHex = ethUtil.bufferToHex(Buffer.from(msg));

            // Check if signature is valid
            const msgBuffer = ethUtil.toBuffer(msgHex);
            const msgHash = ethUtil.hashPersonalMessage(msgBuffer);
            const signatureBuffer = ethUtil.toBuffer(req.body.signature);
            const signatureParams = ethUtil.fromRpcSig(signatureBuffer);
            const publicKey = ethUtil.ecrecover(
                msgHash,
                signatureParams.v,
                signatureParams.r,
                signatureParams.s
            );
            const addressBuffer = ethUtil.publicToAddress(publicKey);
            const address = ethUtil.bufferToHex(addressBuffer);
            
            console.log("Decrypted address: " + address);
            console.log("User address: " + req.params.user);

            // Check if address matches
            if (address.toLowerCase() === req.params.user.toLowerCase()) {
                // Run NFT ownership check if env flag is enabled
                if (process.env.RESTRICT_BY_NFT_COLLECTION == "true") {
                    request.get(`https://api.opensea.io/api/v1/assets?owner=${req.params.user}&collection=${process.env.NFT_COLLECTION_SLUG}`, (err, response, body) => {
                        if (err) {
                            console.error(err.message);
                            return res.status(500).send(err.message);
                        }
                        if (response.statusCode == 200) {
                            if (JSON.parse(body).assets.length >= 0) {
                                console.log("User owns NFT from collection - access granted");

                                // Update user nonce
                                var newNonce = Math.floor(Math.random() * 1000000);
                                db.run('UPDATE users SET nonce = ? WHERE address = ?', [newNonce, req.params.user], (err) => {
                                    if (err) {
                                        console.error(err.message);
                                        return res.status(500).send(err.message);
                                    }
                                    // Set jwt token
                                    const token = jwt.sign({
                                        address: req.params.user,
                                        nonce: newNonce
                                    }, process.env.JWT_SECRET);
                                    return res.status(200).send({
                                        success: true,
                                        token: `Bearer ${token}`,
                                        user: row,
                                        msg: "You are now logged in."
                                    });
                                });

                            } else {
                                console.log("User does not own NFT from collection - access denied");
                                return res.status(403).send("User does not own NFT from collection");
                            }
                        } else {
                            console.log("User does not own NFT from collection");
                            return res.status(403).send("User does not own NFT from collection");
                        }
                    });
                }

                if (process.env.RESTRICT_BY_NFT_COLLECTION == "false") {
                    // Update user nonce
                    var newNonce = Math.floor(Math.random() * 1000000);
                    db.run('UPDATE users SET nonce = ? WHERE address = ?', [newNonce, req.params.user], (err) => {
                        if (err) {
                            console.error(err.message);
                            return res.status(500).send(err.message);
                        }
                        // Set jwt token
                        const token = jwt.sign({
                            address: req.params.user,
                            nonce: newNonce
                        }, process.env.JWT_SECRET);
                        return res.status(200).send({
                            success: true,
                            token: `Bearer ${token}`,
                            user: row,
                            msg: "You are now logged in."
                        });
                    });
                }
            } else {
                return res.status(401).send({
                    success: false,
                    msg: "Signature is invalid."
                });
            }
        } else {
            console.log('User does not exist');
            return res.status(404).send('User not found');
        }
    });
});