index.js

var express = require('express');
var bodyParser = require('body-parser');
var engines = require('consolidate');
var app = express();

var https = require('https');

app.use(bodyParser.urlencoded({ extended: false }));
app.engine('html', engines.hogan);

app.get('/', function(req, res) {
        res.render('form.html');
});

app.post('/register', function(req, res) {
        verifyRecaptcha(req.body["g-recaptcha-response"], function(success) {
                if (success) {
                        res.end("Success!");
                        // TODO: do registration using params in req.body
                } else {
                        res.end("Captcha failed, sorry.");
                        // TODO: take them back to the previous page
                        // and for the love of everyone, restore their inputs
                }
        });
});

app.listen(3000);
console.log("running on port 3000");

var SECRET = "6Ld4*******";

// Helper function to make API call to recatpcha and check response
function verifyRecaptcha(key, callback) {
         https.get("https://www.google.com/recaptcha/api/siteverify?secret=" + SECRET + "&response=g-recaptcha-response", function(res) {
                var data = "";
                res.on('data', function (chunk) {
                        data += chunk.toString();
                });
                res.on('end', function() {
                        try {
                                var parsedData = JSON.parse(data);
                                callback(parsedData.success);
                        } catch (e) {
                                callback(false);
                        }
                });
        });
}

package.json

{
  "name": "captcha",
  "version": "0.0.0",
  "private": true,
   "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "dependencies": {
    "body-parser": "~1.13.2",
    "cookie-parser": "~1.3.5",
    "debug": "~2.2.0",
    "consolidate": "0.13.1",
    "hogan.js": "3.0.2",
    "express": "~4.13.1",
    "jade": "~1.11.0",
    "morgan": "~1.6.1",
    
    "serve-favicon": "~2.3.0"
  }
}

server.js

function verifyRecaptcha(key, callback) {
     https.get("https://www.google.com/recaptcha/api/siteverify?secret=" + SECRET + "&response=g-recaptcha-response", function(res) {
        var data = "";
        res.on('data', function (chunk) {
                        data += chunk.toString();
        });
        res.on('end', function() {
            try {
                var parsedData = JSON.parse(data);
                console.log(parsedData);
                callback(parsedData.success);
            } catch (e) {
                callback(false);
            }
        });
    });
}