For every request a tracking id is generated and printed out with every log entry:

com.openexchange.request.trackingId=1b13e0222f7c4e 0a9170d9301462b856

For clients it is possible to override this id. That enables aggregating log entries for operations that span multiple requests. Therefore a generic request parameter 'trackingId' can be set for every API call.

GET ' on=12345&trackingId=<custom identifier>'