Currently, we are using ${httpRouting.reasonCode} context variable to evaluate the error in routing and sending an appropriate error back to the requestor. However, reason code -5 could have multiple causes. For example, when there is change in the certificate trust chain of the back-end API server, we'll receive -5 routing reason code. Is there a way to capture the exact reason for error, CertificateException in this case, to send it back to the requestor?
All supported versions of the API Gateway
The response -5 undefined is that, undefined. So unfortunately there really is no way to get additional information. If you are using it in conjunction with the ${response.http.status} you may be able to get additional http information, but the response is often the same.