CB-SVRLESS-2 - Initial code to verify FB request

CB-SVRLESS-2-VerificationCode.js

module.exports.fbVerify = (event, context, callback) => {
    if (event.query['hub.mode'] === 'subscribe' &&
        event.query['hub.verify_token'] === 'sometoken') {
        console.log("Validating webhook");
        return callback(null, parseInt(event.query['hub.challenge']));
    } else {
        console.error("Failed validation. Make sure the validation tokens match.");
        return callback('Invalid token');
    }
};