Amazon Cognito User Pools - Custom Message Hook with AWS Lambda (Node.js)

index.js

exports.handler = (event, context, callback) => {
    if(event.userPoolId === "theSpecialUserPool") {
        // check event type
        if(event.triggerSource === "CustomMessage_SignUp") {
            // customize message and subject content
            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";
        }
    }
    callback(null, event);
};