AWS Cognito: Custom Challenge with Retry

Question

I am using Custom Challenge for MFA because i wanted to use Twilio instead of AMAZON SNS. i have successfully implemented it. It works fine but When a user enters wrong OTP code. The user session is expired. means that he has to again provide phone number and request a OTP again. Whereas i want it to retry for atleast 3 time. before he need to request another OTP. My Response verify trigger is as simple as below, is there something that we can do.

(event, context, callback) => {
    if (event.request.privateChallengeParameters.answer == event.request.challengeAnswer) {
        event.response.answerCorrect = true;
    } else {
        event.response.answerCorrect = false;
    }
    callback(null, event);
}

Answer 1

I acheived this by adding the answer as a variable into challengeMetaData - which so far as I can see is not returned to the client but is available on subsequent calls, I also have a variable named attempts to track how many times the user has entered an incorrect value.My code is below - I hope it helps

const AWS = require("aws-sdk");
exports.handler = (event, context, callback) => {

    const session = event.request.session;
    const currentSession = session ? session.length - 1 : 0

    switch (event.triggerSource) {
        case 'DefineAuthChallenge_Authentication':

            console.log("DefineAuthChallenge_Authentication");
            console.log(event);

            if (session.length === 0) {
                event.response = {
                    challengeName: 'CUSTOM_CHALLENGE',
                    failAuthentication: false,
                    issueTokens: false
                };
            }
            else {
                if (session[currentSession].challengeName === 'CUSTOM_CHALLENGE') {

                    if (session[currentSession].challengeResult === true) {
                        event.response.issueTokens = true;
                        event.response.failAuthentication = false;
                    }
                    else {

                        let metaData = JSON.parse(session[currentSession].challengeMetadata);
                        if (metaData.attempts <= 3) {
                            event.response = {
                                challengeName: 'CUSTOM_CHALLENGE',
                                failAuthentication: false,
                                issueTokens: false
                            };
                        }
                        else {
                            event.response.issueTokens = false;
                            event.response.failAuthentication = true;
                        }
                    }
                }
            }
            console.log(event);
            break;
        case 'CreateAuthChallenge_Authentication':
            if (event.request.challengeName === 'CUSTOM_CHALLENGE') {
                console.log("CreateAuthChallenge_Authentication");
                console.log(event);
                if (session.length === 0) {
                    let answer = Math.random().toString(10).substr(2, 6);

//Your logic to send a message goes here
                    
                    event.response.publicChallengeParameters = { challengeType: 'SMS_CODE' };
                    event.response.privateChallengeParameters = { answer: answer };
                    event.response.challengeMetadata = JSON.stringify({ '_sid': answer, 'challengeType': 'SMS_CODE', attempts: 1 });
                }
                else {
                    let metaData = JSON.parse(session[currentSession].challengeMetadata);
                    if (metaData.attempts <= 3) {
                        event.response.publicChallengeParameters = { challengeType: 'SMS_CODE', errorCode: 'NotAuthorizedException' };
                        event.response.privateChallengeParameters = { answer: metaData._sid };
                        event.response.challengeMetadata = JSON.stringify({ '_sid': metaData._sid, 'challengeType': 'SMS_CODE', attempts: metaData.attempts + 1 });
                    }
                }
            }
            console.log(event);
            break;
        default:
            console.log("VerifyAuthChallenge_Authentication");
            console.log(event);
            if (event.request.privateChallengeParameters.answer === event.request.challengeAnswer) {
                event.response.answerCorrect = true;
            }
            else { event.response.answerCorrect = false; }
            console.log(event);
            break;
    }
    callback(null, event);
};