provides a means for the current user to authenticate to access
resources available through the 9P connection represented by
The return value is a file descriptor, conventionally called
that is subsequently used to execute the authentication protocol
for the server.
After successful authentication,
may be passed as the second argument to a subsequent
with the same
as a ticket-of-entry for the user.
returns nil, the error case, that means the file server does not require
authentication for the connection, and
should be nil
in the call to