Bug: TransferFamilyAuthorizer.password raises KeyError when the event has no password #8714

Expected Behaviour

TransferFamilyAuthorizer.password is typed str | None and documented as "None in case customer authenticating with certificates", so an authorizer event without a password should give None. The Pydantic TransferFamilyAuthorizer model already declares password with default=None.

Current Behaviour

The property returns self["password"], so an event without a password key raises KeyError instead of returning None. The custom identity provider examples in the Transfer Family docs read it defensively (event.get('password', '') == '' in Python) to detect key-based logins, which the data class can't do today.

Code snippet

from aws_lambda_powertools.utilities.data_classes import TransferFamilyAuthorizer

event = {"username": "bobusa", "protocol": "SFTP", "serverId": "s-abcd123456", "sourceIp": "192.168.0.100"}
TransferFamilyAuthorizer(event).password  # KeyError: 'password'

Steps to Reproduce

1. Build a TransferFamilyAuthorizer from an event that has no password key.
2. Read .password.
3. KeyError is raised.

Possible Solution

Return self.get("password"), matching the type hint and the Pydantic model. I can open a PR.

Powertools for AWS Lambda (Python) version

latest (develop, 3.38.0)

AWS Lambda function runtime

3.12

Packaging format used

PyPi

Debugging logs

No response