Sign in failed AuthError: Invalid lambda function output : Invalid JSON - amazon-web-services

Question

I am attempting to set up passwordless sms authentication using amplify in an IOS project. I have lambda triggers taken from a github repo set up this way:
CreateAuthChallenge
// ### About this Flow ###
// Using Custom Auth Flow through Amazon Cognito User Pools with Lambda Triggers to complete a 'CUSTOM_CHALLENGE'.
//
// ### About this function ###
// This CreateAuthChallengeSMS function (2nd of 4 triggers) creates the type of 'CUSTOM_CHALLENGE' as a one-time pass code sent via SMS. A one-time randomly generated 6-digit code (passCode)
// is sent via SMS (through Amazon SNS) to the user's mobile phone number during authentication. The generated passCode is stored in privateChallengeParameters.passCode and passed to the VerifyAuthChallenge function
// that will verify the user's entered passCode (received via SMS) into the mobile/web app matches the passCode passed privately through privateChallengeParameters.passCode.
// ### Next steps ###
// Instead of using the "crypto-secure-random-digit" library to generate random 6-digit codes, create a base32 secret for the user (if not exist) and
// generate a 6-digit code based on this secret. Much like TOTP except for the secret is never shared with the user. With a base32 secret associated with the user,
// we can easily switch from 6-digit code via SMS to 6-digit code generated based on shared secret via TOTP using the OATH module of a YubiKey or an authenticator app.
//
// Updated: Jan 6, 2020
'use strict';
const crypto_secure_random_digit = require("crypto-secure-random-digit");
const AWS = require("aws-sdk");
var sns = new AWS.SNS();
// Main handler
exports.handler = async (event = {}, context, callback) => {
console.log('RECEIVED event: ', JSON.stringify(event, null, 2));
let passCode;
var phoneNumber = event.request.userAttributes.phone_number;
// The first CUSTOM_CHALLENGE request for authentication from
// iOS AWSMobileClient actually comes in as an "SRP_A" challenge (a bug in the AWS SDK for iOS?)
// web (Angular) comes in with an empty event.request.session
if (event.request.session && event.request.session.length && event.request.session.slice(-1)[0].challengeName == "SRP_A" || event.request.session.length == 0) {
passCode = crypto_secure_random_digit.randomDigits(6).join('');
await sendSMSviaSNS(phoneNumber, passCode);
} else {
const previousChallenge = event.request.session.slice(-1)[0];
passCode = previousChallenge.challengeMetadata.match(/CODE-(\d*)/)[1];
}
event.response.publicChallengeParameters = { phone: event.request.userAttributes.phone_number };
event.response.privateChallengeParameters = { passCode };
event.response.challengeMetadata = `CODE-${passCode}`;
console.log('RETURNED event: ', JSON.stringify(event, null, 2));
callback(null, event)
};
// Send secret code over SMS via Amazon Simple Notification Service (SNS)
async function sendSMSviaSNS(phoneNumber, passCode) {
const params = { "Message": "[Mapwork] Your secret code: " + passCode, "PhoneNumber": phoneNumber };
await sns.publish(params).promise();
}
DefineAuthChallenge
// ### About this Flow ###
// Using Custom Auth Flow through Amazon Cognito User Pools with Lambda Triggers to complete a 'CUSTOM_CHALLENGE'. This is the same flow as one-time passcode generated and sent via SMS or Email.
// Instead, the service and user share a secret that was created during registration and both generate a 6-digit code based on the shared secret.
// If the two codes (typically only good for 30 seconds) match, the user is authenticated.
//
// ### About this function ###
// This DefineAuthChallengeCustom function (1st and 4th of 4 triggers) defines the type of challenge-response required for authentication.
// For HOTP, TOTP, U2F, or WebAuthn flows, we'll always use 'CUSTOM_CHALLENGE' and this function code won't change between the various auth methods.
// ### Next steps ###
// Updated: June 12, 2020
'use strict';
exports.handler = async (event) => {
console.log('RECEIVED event: ', JSON.stringify(event, null, 2));
// The first auth request for CUSTOM_CHALLENGE from the AWSMobileClient (in iOS native app) actually comes in as an "SRP_A" challenge (BUG in AWS iOS SDK), so switch to CUSTOM_CHALLENGE and clear session.
if (event.request.session && event.request.session.length && event.request.session.slice(-1)[0].challengeName == "SRP_A") {
console.log('New CUSTOM_CHALLENGE', JSON.stringify(event, null, 2));
event.request.session = [];
event.response.issueTokens = false;
event.response.failAuthentication = false;
event.response.challengeName = 'CUSTOM_CHALLENGE';
}
// User successfully answered the challenge, succeed with auth and issue OpenID tokens
else if (event.request.session &&
event.request.session.length &&
event.request.session.slice(-1)[0].challengeName === 'CUSTOM_CHALLENGE' &&
event.request.session.slice(-1)[0].challengeResult === true) {
console.log('The user provided the right answer to the challenge; succeed auth');
event.response.issueTokens = true;
event.response.failAuthentication = false;
}
// After 3 failed challenge responses from user, fail authentication
else if (event.request.session && event.request.session.length >= 4 && event.request.session.slice(-1)[0].challengeResult === false) {
console.log('FAILED Authentication: The user provided a wrong answer 3 times');
event.response.issueTokens = false;
event.response.failAuthentication = true;
}
// The user did not provide a correct answer yet; present CUSTOM_CHALLENGE again
else {
console.log('User response incorrect: Attempt [' + event.request.session.length + ']');
event.response.issueTokens = false;
event.response.failAuthentication = false;
event.response.challengeName = 'CUSTOM_CHALLENGE';
}
console.log('RETURNED event: ', JSON.stringify(event, null, 2));
return event;
};
VerifyAuthChallenge
// ### About this Flow ###
// Using Custom Auth Flow through Amazon Cognito User Pools with Lambda Triggers to complete a 'CUSTOM_CHALLENGE'. This custom challenge is using
// a randomly generated 6-digit sent to the user via SMS using Amazon SNS.
//
// ### About this function ###
// This VerifyAuthChallengeSMS function (3rd of 4 triggers) takes the user's 6-digit code sent via event.request.challengeAnswer parameter
// and returns TRUE if the user's passCode matches event.request.privateChallengeParameters.passCode.
// ### Next steps ###
'use strict';
exports.handler = async (event) => {
console.log('RECEIVED Event: ', JSON.stringify(event, null, 2));
let expectedAnswer = event.request.privateChallengeParameters.passCode || null;
if (event.request.challengeAnswer === expectedAnswer) {
event.response.answerCorrect = true;
}
else {
event.response.answerCorrect = false;
}
console.log('RETURNED Event: ', JSON.stringify(event, null, 2));
return event;
};
And then I invoke Auth.signIn() from the ios mobile device. However,I receive this error when I do so:
Sign in failed AuthError: Invalid lambda function output : Invalid JSON
I have been struggling for hours with this one and any help would be appreciated.