GSI authentication involves an encoded TLS/SSL handshake over the FTP
control session. Decoding the exchanged tokens and passing them to an
SSL analyzer instance allows use of all the familiar script-layer events
in inspecting the handshake (e.g. client/server certificats are
available). For FTP sessions that attempt GSI authentication, the
service field of the connection record will have both "ftp" and "ssl".
One additional change is an FTP server's acceptance of an AUTH request
no longer causes analysis of the connection to cease (because further
analysis likely wasn't possible). This decision can be made more
dynamically at the script-layer (plus there's now the fact that further
analysis can be done at least on the GSSAPI AUTH method).
It relies on the heuristics of GridFTP data channels commonly default to
SSL mutual authentication with a NULL bulk cipher and that they usually
transfer large datasets (default threshold of script is 1 GB). The
script also defaults to skip_further_processing() after detection to try
to save cycles analyzing the large, benign connection.
Also added a script in base/protocols/conn/polling that generalizes the
process of polling a connection for interesting features. The GridFTP
data channel detection script depends on it to monitor bytes
transferred.
