🌱Post confirmation trigger

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🌱Post confirmation trigger

This is a digital garden post

Michael Liendo's photo
Michael Liendo
·Aug 4, 2022·

This is a digital garden post. This means I may come back and "water" it by making this look pretty, but for right now it's just a wee sprout 🌱

purpose: I needed to add an authenticated user to a database when they signup but when constructing the event in the lambda, I didn't know the details of what the event object contained. So I spent all of 15 minutes to create this example.

The CLI command:

npx create-next-app trigger-example && cd $_ && npm i aws-amplify @aws-amplify/ui-react && amplify init -y && amplify add auth

select yes to configure auth with defaults

amplify push -y

Once done pushing:

amplify update auth

Go through all the options, selecting the defaults along the way.

When asked if I want to update the attributes, I selected email, name, family name, and if I remember right username unless that is just a given attribute.

The very last option is to add a trigger. Say yes. Create your own module. Select edit function

Note that the code gets put in a custom.js file and isn't the index.js file.

Put in the following code:

 * @type {import('@types/aws-lambda').APIGatewayProxyHandler}
exports.handler = async (event, context) => {
    // insert code to be executed by your lambda trigger
    console.log('the current user info', JSON.stringify(event, null, 2))
    return event

Update your _app.js file:

import { Amplify } from 'aws-amplify'
import { AmplifyProvider } from '@aws-amplify/ui-react'
import '@aws-amplify/ui-react/styles.css'
import config from '../src/aws-exports'

function MyApp({ Component, pageProps }) {
    return (
            <Component {...pageProps} />

export default MyApp

Update your index.js file:

import { Button, withAuthenticator } from '@aws-amplify/ui-react'

function Home({ signOut }) {
    return <Button onClick={signOut}>Signout</Button>

export default withAuthenticator(Home)

The result is that the default login UI looks like this when signing up for an account:


Once you login, the output for your user looks like the following in CloudWatch:


delete it all: amplify delete

If wanting to update a dynamoDB table:

const AWS = require('aws-sdk')
const docClient = new AWS.DynamoDB.DocumentClient()

async function main(event) {
    //construct the params
    const params = {
        TableName: process.env.TABLENAME,
        Item: {
            id: event.request.userAttributes.sub,
            firstname: event.request.userAttributes.name,
            lastname: event.request.userAttributes.family_name,
            username: event.userName,
            email: event.request.userAttributes.email,

    //try to add to the DB, otherwise throw an error
    try {
        await docClient.put(params).promise()
        return event
    } catch (err) {
        return event

module.exports = { main }
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