Cognito custom-message triggered lambda returns InvalidLambdaResponseException - amazon-web-services

Question

I've created a lambda and assigned it to cognito throw the UI as its custom-message lambda.
Here is the code in typescript:
export const handler = async (event) => {
const trigger = event.triggerSource
const customMessage = cloneDeep(customMessages[trigger])
if (customMessage) {
try {
// inject cognito values to custom message
const codeParameter = event.request.codeParameter
const usernameParameter = event.request.usernameParameter
for (let key in customMessage) {
let text = customMessage[key]
if (codeParameter) {
customMessage[key] = text.replace(/{{codeParameter}}/g, codeParameter)
}
if (usernameParameter) {
customMessage[key] = text.replace(/{{usernameParameter}}/g, usernameParameter)
}
}
// load HTML template
let htmlFile = readFileSync(templateFilePath, { encoding: 'utf8' })
htmlFile = htmlFile.replace(/(\r\n|\n|\r)/gm, '')
const template = handlebars.compile(htmlFile)
const html = template(customMessage)
event.emailMessage = html
event.response.emailSubject = customMessage.title
} catch (err) {
logger.error(err)
return event
}
}
return event
}
Basically it loads an html template file and injects the code-parameters and username.
now the response our signup flow lambda returns is:
{
"message": "InvalidLambdaResponseException",
"details": "Unrecognizable lambda output"
}
I event tried to copy paste AWS example:
exports.handler = (event, context, callback) => {
//
if(event.userPoolId === "theSpecialUserPool") {
// Identify why was this function invoked
if(event.triggerSource === "CustomMessage_SignUp") {
// Ensure that your message contains event.request.codeParameter. This is the placeholder for code that will be sent
event.response.smsMessage = "Welcome to the service. Your confirmation code is " + event.request.codeParameter;
event.response.emailSubject = "Welcome to the service";
event.response.emailMessage = "Thank you for signing up. " + event.request.codeParameter + " is your verification code";
}
// Create custom message for other events
}
// Customize messages for other user pools
// Return to Amazon Cognito
callback(null, event);
};
The response is the same.
Any suggestions?
Thanks

Answer 1

Here is my custom message lambda. It runs on Node 8.10. Maybe you'd like to test/adapt it. I've stripped some other stuff out but it should work fine
exports.handler = function(event, context) {
const cognitoUserPool = 'us-east-1_AAAAAA';
const snsTopicArn = 'arn:aws:sns:us-east-1:9999999999:BBBBBBBBBB';
const baseurl = 'https://company.us-east-1.elasticbeanstalk.com/app';
console.log('Cognito Event:', event);
var AWS = require("aws-sdk");
if(event.userPoolId === cognitoUserPool) {
if(event.triggerSource === "CustomMessage_SignUp") {
event.response.emailSubject = "Welcome to Company";
event.response.emailMessage = "Hello etc";
context.done(null, event);
}
if(event.triggerSource === "CustomMessage_ResendCode") {
event.response.emailSubject = "Welcome to Company";
event.response.emailMessage = "Some other message etc";
context.done(null, event);
}
if(event.triggerSource === "CustomMessage_ForgotPassword") {
event.response.emailSubject = "Your password reset";
event.response.emailMessage = "Some other message again etc";
context.done(null, event);
}
// Other event types can go here
} else {
context.done(null, event);
}
};