Curl now supports Kerberos with a --krb flag:
(FTP) Enable Kerberos authentication and use. The level must be entered and should be one of 'clear', 'safe', 'confidential' or 'private'. Should you use a level that is not one of these, 'private' will instead be used.
This option requires that the library was built with kerberos4 or GSSAPI (GSS-Negotiate) support. This is not very common. Use -V/--version to see if your curl supports it.
If this option is used several times, the last one will be used.
Can this be incorporated into CurlFtpFS?