Unable to add custom claims to authentication token with PowerTools v3.9.0 and later

[ogis-takeuchi]

Hello,

The following process worked correctly with PowerTools for AWS Lambda (Python) v3.8.0 and earlier, but since v3.9.0, the response in the returned raw_event no longer contains the custom claims.

I would like to avoid directly editing the raw_event dictionary. Is there any recommended way to add custom claims to the authentication token in v3.9.0 or later?

Here is a simplified version of my handler:

from aws_lambda_powertools.utilities.data_classes.cognito_user_pool_event import PreTokenGenerationV2TriggerEvent

def lambda_handler(event: dict, context: LambdaContext) -> dict:
    pre_token_generation = PreTokenGenerationV2TriggerEvent(event)
    # Add custom_user_id to both ID and Access tokens
    pre_token_generation.response.claims_scope_override_details.id_token_generation = {
        'claimsToAddOrOverride': {
            'custom_user_id': pre_token_generation.request.user_attributes['preferred_username'],
        }
    }
    pre_token_generation.response.claims_scope_override_details.access_token_generation = {
        'claimsToAddOrOverride': {
            'custom_user_id': pre_token_generation.request.user_attributes['preferred_username'],
        }
    }
    # Return the raw event
    return pre_token_generation.raw_event

Difference in raw_event between v3.8.0 and v3.9.0
■v3.8.0 raw_event example:

{
  'version': '2',
  'region': 'example-region-1',
  ...,
  'response': {
    'claimsAndScopeOverrideDetails': {
      'idTokenGeneration': {
        'claimsToAddOrOverride': {
          'custom_user_id': 'user123'
        }
      },
      'accessTokenGeneration': {
        'claimsToAddOrOverride': {
          'custom_user_id': 'user123'
        },
        'scopesToAdd': ['access:example_scope']
      }
    }
  }
}

■v3.9.0 raw_event example:

{
  'version': '2',
  'region': 'example-region-1',
  ...,
  'response': {}

}
With v3.9.0 and later, the returned event does not contain the expected values in response.
Is there a way to add custom claims without directly modifying the raw event dictionary?
If there is a new recommended approach or migration guide for this use case, I would appreciate your advice.

Environment:
AWS Lambda (Python3.13)
PowerTools for AWS Lambda (Python) v3.9.0
Cognito Pre Token Generation Trigger
Lambda deployment: Container image (not Zip package)