In your DokuWiki installation, create a folder lib/plugins/authfluxbb/ and create the two files auth.php and plugin.info.txt in it.
In your wiki's conf/local.protected.php (create this file if it does not exist), add the following lines:
$conf['authtype'] = 'authfluxbb';
$conf['superuser'] = '@Administrators,@Moderators';
// Make sure stripping slashes doesn't clash with the forums.
if (!defined('FORUM_DISABLE_STRIPSLASHES'))
define('FORUM_DISABLE_STRIPSLASHES', 1);
// Connect with FluxBB
define('PUN_ROOT', dirname(__FILE__).'/../../');
include_once PUN_ROOT.'include/common.php';
NOTE: Be sure to overwrite the value of PUN_ROOT with the location of your FluxBB installation, relative to the configuration file. (The above example would work if the forum would be located in / and the wiki in /docs/.)
The variable $conf['superusers'] can be used to set the names of the FluxBB groups that have superuser access to the wiki.