authentication
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... commands and responses have been
included. This is not to imply that other commands (including
authentication, directory modification, PORT or PASV commands, or
similar) would not be present in an actual connection ...
... Servers are not required to accept "OPTS MLST" commands before
authentication of the user-PI, but may choose to permit them.
...
... FEAT and OPTS commands may be issued before the FTP
authentication has occurred [6]. This allows unauthenticated clients
...
... MLSx commands may
be issued however, and no problems with permitting the selection of
the format prior to authentication are foreseen.
A general discussion ...