It doesn't. That's also the downside of most login/identity providers that implement some form of "Impersonation."

Without really smart and well-considered limitations and logging, it's impossible to tell the User from the User* without digging through audit trails, etc.. and if the developers/architects involved didn't consider the limitations and logging in the first place, odds are they didn't consider the audit trails either.

And yes, I do this for a living.. and have seen bad things from major organizations. :(