VMS Help TCPIP Services, Programming Interfaces, RPC XDR Routines, xdr_opaque_auth, Arguments  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 xdrs
    A pointer to an XDR stream handle created by one of the XDR
    stream handle creation routines.
 authp
    A pointer to an opaque_auth structure describing authentication
    information. The pointer should reference data created by the
    authnone_create, authunix_create, or authunix_create_default
    routine.