CreateAuthChallenge.js

exports.handler = (event, context, callback) => {
    console.log('-- event', JSON.stringify(event))
    
    if (!event.request.session || event.request.session.length === 0) {
        event.response.publicChallengeParameters = {
            publicParam: "url/123.jpg", // whatever you want
        };
        // Something code that send the PIN to phone
        event.response.privateChallengeParameters = {
            answer: "1234", // PIN
        };
        event.response.challengeMetadata = "PIN_CHALLENGE";
    }
    callback(null, event);
}