Is it possible to get the user id of the sender in an agentX suba gent?

I am porting a legacy app that supports a couple of mibs to linux and I am
replacing the old snmp code with net-snmp.  I've used mib2c to generate all
the callback routines in my agentX subagent.  The old snmp code (v1, v2
only) did some access restriction based upon the user id, which they just
extracted from the pdu.  It doesn't appear that I have access to the pdu or
the userID in my callback routines.  Does anyone know of a way to access
this information in the agentX modules?
 
Thanks
chris