Stuck with a Cognito Post-Confirmation Lambda trigger that does not work!

Hello guys, I have written a Lambda function of a few Python lines which, when it try to assign a self-registered user to a default group immediately after registration, tells me that the user does not exist. The Lambda, has a role with the following permissions:

• cognito-idp:AdminGetUser
• cognito-idp:ListUsers
• cognito-idp:GetGroup
• cognito-idp:AdminAddUserToGroup

When a person self-registers, the user is set into the User Pool, then confirmed by sending/receiving the activation code. Unfortunately the Lambda trigger returns an error and does not add the user the group.

This is the Lambda I'm using:

    import boto3
    def lambda_handler(event, context):
    try:

    # Log the entire event to inspect its structure

    print(f"Received event: {event}")

    # Extract user information from the event

    user_attributes = event.get("request", {}).get("userAttributes", {})

    # Log the userAttributes dictionary

    print(f"userAttributes: {user_attributes}")

    # Check if 'sub' is present in userAttributes

    if "sub" not in user_attributes:

        raise ValueError("User ID (sub) not found in userAttributes")

    username = user_attributes["sub"]  # User ID

    # Add the user to the "default" group in Cognito User Pool

    user_pool_id = "eu-south-1_*********"

    group_name = "users"

    client = boto3.client("cognito-idp")

    # Check if the user exists before adding to the group

    try:

        client.admin_get_user(UserPoolId=user_pool_id, Username=username)

    except client.exceptions.UserNotFoundException:

        print(f"User {username} not found in the User Pool. Skipping group assignment.")

        return event

    # Add the user to the group

    response = client.admin_add_user_to_group( UserPoolId=user_pool_id, Username=username, GroupName=group_name )

    print(f"User {username} added to group {group_name}")

    return event

# except ValueError(s) are omitted. . . 

For the sake of completeness, I also enclose the entire set of logged events:

START RequestId: d5d3be28-70e5-4f56-ad12-48b2f26bdf00 Version: $LATEST Received event: { 'version': '1', 'region': 'eu-south-1', 'userPoolId': 'eu-south-1_#########, 'userName': 'G**.N***', 'callerContext': { 'awsSdkVersion': 'aws-sdk-unknown-unknown', 'clientId': '5sqdae#########' }, 'triggerSource': 'PostConfirmation_ConfirmSignUp', 'request': { userAttributes': { 'sub': 'f6ce52c0-1091-7032-8f7b-353e8ae07cc9', 'email_verified': 'true', 'cognito:user_status': 'CONFIRMED', 'name': 'Giselle Normand', 'email': 'g***@***.com' } }, 'response': {} }

userAttributes: {'sub': 'f6ce52c0-1091-7032-8f7b-353e8ae07cc9', 'email_verified': 'true', 'cognito:user_status': 'CONFIRMED', 'name': 'Giselle Normand', 'email': 'g***@***.com'}

User f6ce52c0-1091-7032-8f7b-353e8ae07cc9 not found in the User Pool. Skipping group assignment.**

END RequestId: d5d3be28-70e5-4f56-ad12-48b2f26bdf00

Any idea why this Lambda fails?

THX Ste

PS I can't understand the reason of: 'aws-sdk-unknown'; everything runs within AWS services and BOTO3 is the latest AWS-SDK for Python PS2 be forgiving, per cortesia, this is the first time I got my hands on AWS