I've never seen anyone store salts in a separate table - that's pretty weird. The salt is normally appended to the password, and the two stored together in the same table column.

So, what you would normally see looks more like this:

 __PACKAGE__->authen->config(
     DRIVER => [ 'DBI',
         DBH         => $dbh,   # provide your own DBI handle
         TABLE       => 'user',
         CONSTRAINTS => { 'user.name'      => '__CREDENTIAL_1__' }
         COLUMNS     => { 'crypt:password' => '__CREDENTIAL_2__' },
     ],
 );
[download]

Note that there's only one table, so there's no need for a join, but since the password is encoded, you need a 'COLUMNS' field.

But what you really want is MD5 encryption. To do that, you need to write a custom filter using Crypt::PasswdMD5, call it cryptmd5, then use it like this:

__PACKAGE__->authen->config(
     DRIVER => [ 'DBI',
         DBH         => $dbh,   # provide your own DBI handle
         TABLE       => 'user',
         CONSTRAINTS => { 'user.name'      => '__CREDENTIAL_1__' }
         COLUMNS     => { 'cryptmd5:password' => '__CREDENTIAL_2__' },
         FILTERS     => { cryptmd5 => \&cryptmd5_filter },
     ],
 );
[download]

Implement cryptmd5_filter just like crypt_filter (see the CGI::Application::Plugin::Authentication::Driver::Filter::crypt source), only replace crypt() with unix_md5_crypt(). I think that will do what you want.