example code for: https://medium.com/aws-factory/recaptcha-form-with-an-amazon-aws-backend-based-on-cdk-78377db58d1f

contactForm.ts

import Sns from "aws-sdk/clients/sns";
import axios from 'axios';
import * as querystring from 'querystring';

const reCapUrl = "https://www.google.com/recaptcha/api/siteverify";

// we got this from personal reCaptcha Google Page
const reCaptchaSecret = "xxxxxxxxxxxxxxxxxxxxxxxx" ;

function bodyToMap(parts: any) : Map<String, String>{
    let result = new Map();
    // grab the params
    for (let i = 0, len = parts.length; i < len; i++) {
        let kVal = parts[i].split('=');
        // replace the + space then decode
        let key = decodeURIComponent(kVal[0].replace(/\+/g, ' '));
        result.set(key, decodeURIComponent(kVal[1].replace(/\+/g, ' ')));
    }
    return result;
}

export const handler = async (event: any = {}): Promise<any> => {
    console.log("Starting ContactForm Processing for website okaycloud form.");

    let body = event.body;
    // process the urlencoded body of the form submit and put it in a
    // map structure
    let parts = body.split('&');
    let result = bodyToMap(parts);

    // its always a good idea to log so that we can inspect the params
    // later in Amazon Cloudwatch
    //console.log(result);

    let data = querystring.stringify({
        secret: reCaptchaSecret,
        response: result.get("g-recaptcha-response")
    });

    //console.log(`Verify Post Data: ${JSON.stringify(data)}`);
    //console.log(`Verify Post Data Form Encoded: ${data}`);

    // verify the result by POSTing to google backend with secret and
    // frontend recaptcha token as payload
    let verifyResult = await axios.post(reCapUrl, data);

    // if you like you can also print out the result of that. Its
    // a bit verbose though
    //console.log(`Success ist: ${JSON.stringify(verifyResult.data)}`);

    if (verifyResult.data.success) {
        let emailbody = `—— Contactform —-
            
            Name: ${result.get('FULLNAME')} 
            
            Email: ${result.get('EMAIL')}
            Tel: ${result.get('PHONE')}
            
            Thema: ${result.get('SUBJECT')}
            
            * Nachricht * 
            ${result.get("MESSAGE")}
         `;

        let sns = new Sns();

        let params = {
            Message: emailbody,
            Subject: `Contactform:  ${result.get("SUBJECT")}`,
            TopicArn: process.env.TOPIC_ARN
        };

        // we publish the created message to Amazon SNS now…
        await sns.publish(params).promise();

        // now we return a HTTP 302 together with a URL to redirect the
        // browser to success URL (we put in google.com for simplicty)
        return {
            statusCode: 302,
            headers: {
                Location: "https://mydomain.com/contact_success.html",
            }
        };
    } else {
        console.log("reCaptcha check failed. Most likely SPAM.");
        return {
            statusCode: 302,
            headers: {
                Location: "https://mydomain.com/contact_failure.html",
            }
        };
    }
};