for business requirements, we need to send the advertising ID (Google's ADID or Apple's IDFA) to a 3rd party API. We've noticed though that in the context variables there is no mention about this information.
Is it perhaps a "hidden" context variable we can use, or it's not available at all? Would it be possible to expose it without needing to change the applications' source code?
Starting with Mobile SDK v4.6.0 you can configure postbacks to send data to a third party server and use template expansions for populating the advertising identifier value. Find more details here: Postbacks Overview.