Roundcube is a beautiful IMAP webmail client. In order to integrate is properly with an enterprise TWiki installation, ’single authentication’ needed to be implemented – so that the sign-on for TWiki (which is htpasswd style authenticated by lighttpd) can be used for the roundcube authentication seamlessly.
Since the TWiki login/passwords are different from the IMAP [...]

Using twiki with lighttpd is not yet as simple as it should be. One particular problem is that twiki writes out htpasswd files that lighttpd doesn’t parse correctly (twiki includes an unnecessary ‘:$email’ entry).
To fix the problem (so that users can manage their own passwords) here’s a quick fix for {twiki}/lib/TWiki/Users/HtPasswdUser.pm :
sub _dumpPasswd { [...]