Help with AWS Lambda Function for Amazon Cognito Authentication Using USER_PASSWORD_AUTH

Hello Community,

I'm working on an AWS Lambda function to authenticate users with Amazon Cognito using the USER_PASSWORD_AUTH flow. Despite following the documentation and making sure my setup in the AWS Cognito User Pool is correct, I've encountered several issues, initially with the USER_SRP_AUTH flow and now trying to switch to a simpler USER_PASSWORD_AUTH flow for authentication.

The Lambda function is supposed to receive a username and password, calculate a secret hash using the client secret, and then use these to authenticate against Cognito. However, I've faced errors related to the secret hash not matching and missing required parameters when I was attempting the SRP flow. I've corrected the algorithm from RS256 to sha256 for the secret hash calculation, ensured the username and client credentials are correct, and now I am trying to implement the USER_PASSWORD_AUTH flow to simplify the process.

Here's the gist of my current Lambda function:

const AWS = require('aws-sdk');
const crypto = require('crypto');

// Configuration variables
const clientId = 'YOUR_COGNITO_APP_CLIENT_ID';
const clientSecret = 'YOUR_COGNITO_APP_CLIENT_SECRET';

exports.handler = async (event) => {
    const username = event.username; // Assuming these are passed in the event
    const password = event.password;

    // Calculate secret hash
    const secretHash = calculateSecretHash(clientId, clientSecret, username);

    // Setup params for initiateAuth call
    const params = {
        AuthFlow: 'USER_PASSWORD_AUTH',
        ClientId: clientId,
        AuthParameters: {
            USERNAME: username,
            PASSWORD: password,
            SECRET_HASH: secretHash
        },
    };

    try {
        const cognitoIdentityServiceProvider = new AWS.CognitoIdentityServiceProvider();
        const data = await cognitoIdentityServiceProvider.initiateAuth(params).promise();
        // Handle successful authentication
    } catch (err) {
        console.error('Authentication error:', err);
        // Handle errors
    }
};

function calculateSecretHash(clientId, clientSecret, username) {
    const hmac = crypto.createHmac('sha256', clientSecret);
    hmac.update(username + clientId);
    return hmac.digest('base64');
}

I've ensured that my Cognito User Pool and App Client settings are configured to allow USER_PASSWORD_AUTH. However, I've encountered various errors during implementation, from "SecretHash does not match" to "Missing required parameter SRP_A" when attempting the SRP flow.

Questions:

1. Are there common pitfalls or overlooked configurations in setting up Lambda for Cognito authentication using USER_PASSWORD_AUTH?
2. How can I ensure that the secret hash calculation is always correct and matches what Cognito expects?
3. Any suggestions on debugging methods or tools that can help isolate and resolve these authentication issues?
4. Any advice, insights, or references to documentation would be greatly appreciated. Thank you in advance for your help!