NAME
datagram_challenge - set the datagram challenge
SYNOPSIS
void datagram_challenge(string challenge)
DESCRIPTION
Set the datagram challenge for the current binary user object. The
client must send this challenge in order to open the datagram channel,
after which open_datagram() will be called in the object. All
outstanding challenges must be unique.
ERRORS
An error will result if a challenge has already been set for the
current object.