API Gateway defines a [context variable](https://docs.aws.amazon.com/apigateway/latest/developerguide/api-gateway-mapping-template-reference.html#context-variable-reference) `$context.identity.principalOrgId`. This is missing in the java data model: https://github.com/aws/aws-lambda-java-libs/blob/master/aws-lambda-java-events/src/main/java/com/amazonaws/services/lambda/runtime/events/APIGatewayProxyRequestEvent.java#L429. In the json passed from APIGW, this is an optional field within the `RequestIdentity` object.