Diving Deeper: Building a Scalable AWS Amplify Gen 2 Backend for Hero FAQ – Part 2

				
					// amplify/auth/post-confirmation/handler.ts
import type { PostConfirmationTriggerHandler } from "aws-lambda";
import { type Schema } from "../../data/resource";
import { Amplify } from "aws-amplify";
import { generateClient } from "aws-amplify/data";
import { getAmplifyDataClientConfig } from '@aws-amplify/backend/function/runtime';
import { env } from "$amplify/env/post-confirmation";
import { profileGroups } from './../profileGroups';
import {
    CognitoIdentityProviderClient,
    AdminAddUserToGroupCommand
} from '@aws-sdk/client-cognito-identity-provider';

// Configure Amplify client for Lambda environment
const { resourceConfig, libraryOptions } = await getAmplifyDataClientConfig(env);
Amplify.configure(resourceConfig, libraryOptions);

const client = generateClient<Schema>();
const cognitoClient = new CognitoIdentityProviderClient();

async function addUserToGroup(username: string, userPoolId: string): Promise<void> {
    const command = new AdminAddUserToGroupCommand({
        GroupName: profileGroups.USER, // Assign new users to the default 'USER' group
        Username: username,
        UserPoolId: userPoolId
    });

    try {
        const response = await cognitoClient.send(command);
        console.log("User added to Cognito group", { requestId: response.$metadata.requestId });
    } catch (error) {
        console.error("Failed to add user to group:", error);
        throw error; // Re-throw to ensure the error is logged and potentially retried
    }
}

export const handler: PostConfirmationTriggerHandler = async (event) => {
    const userId = event.request.userAttributes.sub;
    const email = event.request.userAttributes.email;
    const username = event.userName;
    const userPoolId = event.userPoolId;

    console.log("Post confirmation event received:", { userId, email, username, userPoolId });

    // Track operations for better error handling and transparency
    const operations = {
        userCreated: false,
        groupAssigned: false
    };

    try {
        // Create user profile in our database (DynamoDB via Amplify Data)
        await client.models.userModel.create({
            userId,
            email,
            createdAt: new Date().toISOString(),
            updatedAt: new Date().toISOString()
        });
        operations.userCreated = true;
        console.log("User profile created in data store");

    } catch (error) {
        console.error("Error creating user profile in data store:", error);
        // Important: Do NOT re-throw here. If user profile creation fails,
        // we still want the user's Cognito account to be confirmed.
    }

    try {
        // Add user to the default Cognito group
        await addUserToGroup(username, userPoolId);
        operations.groupAssigned = true;
    } catch (groupError) {
        console.error("Failed to add user to default group:", groupError);
        // Do NOT re-throw. Group can be manually assigned later if this fails.
    }

    // Log the final status of all post-confirmation operations
    console.log("Post-confirmation operations summary:", operations);

    // Always return the event to allow successful user registration completion
    return event;
};