Support for SNS Custom Resource Handling

I'd like to use this handler with an SNS triggered custom resource, to handle a multi account scenario rather than to lambda in the local account.

In theory the sns message content delivered to lambda in a remote account could be handled in the same way as this but would have been through custom resource in CF > SNS Remote > Lambda i.e rather than dealing with the event directly, something like json.loads(event['Records'][0]['Sns']['Message'])? It would be great to be able to use this handler in that scenario.

Review the handler's existing event processing and the SNS message shape described in the issue, especially event['Records'][0]['Sns']['Message']. Confirm how the CloudFormation > SNS Remote > Lambda path should be represented, then define and test the supported behavior for that scenario.

Written by the indexing model from the issue text.