I can't understand your question
Is there a list of data fields saved in ClientContext?
Anyway, the clientContext contents are documented in the notifyNewSession javadoc.

You are right. There is no way to strictly associate a call to notifyUser with the calls to notifyNewSession and other methods related with the management of the same session request, hence the httpHeaders argument cannot be exported to those methods.
We introduced httpHeaders to support authentication based on cookies, but we thought that authorization tasks would not depend on such information after the user identity had been checked.

We will close this gap in the next release.
In the meantime, you might try to differentiate client requests by decorating the user name on the client side in some way.