Is there a function for setting supllementary groups? I don't see a method 
documented in Process.

I want the equivalent of man (2) setgroups:

 - Function: int setgroups (size_t COUNT, gid_t *GROUPS)
     This function sets the process's supplementary group IDs.  It can
     only be called from privileged processes.  The COUNT argument
     specifies the number of group IDs in the array GROUPS.