I can't, because we're blocked trying to implement this functionality.
In ACS:
If you want to integrate Campaign and AEM, you have to open a ticket with support to reset the password on a system account. We're still waiting on that. The documentation does not make it clear that this requires a support ticket.
If you want to access the REST API manually, the documentation says you need access to Adobe I/O, which so far seems to require opening a support ticket. We're still waiting on that. Again, documentation was not very clear.
My client doesn't pay for Forms, and our engineers are worried this integration may require Forms, so we can't go ahead with any of this until we can make a Proof-of-Concept. We're totally blocked on that. We're a high-level Adobe partner. I feel sorry for companies just getting started at this.
I suspect that due to this lack of documentation, we're eventually just going to try to access the API manually by creating our own AEM Components which will connect to the REST API. Both sides will be https:// and communicate via POST. But again, that's assuming we can get access, which we're still blocked on right now.
Also if you didn't know: Due to privacy concerns, you should now be using an ID to refer to users at all times, when possible. So for instance if we need to insert a link into an email to refer the user back to our side, we might use the parameter "?id=1234" instead of "?email=e@mail.com", so that it can safely be sent in an insecure fashion.