I don't know of such a bridge. What kind of ISPConfig users do you mean? Users for the control panel (e.g. clients and resellers), or system users?
What I was thinking is that if you add a user to drupal it could populate the ispconfig data. There could be a drupal module that calls to the api for ispconfig. The admin of drupal would configure the module to know which ispconfig client to configure. For example web38_xxx then when I add the drupal user testuser It creates the web38_testuser in ispconfig and sets up the same password as the drupal user. Then if I change or delete the user and or password it is updated in ispconfig as well.
I have no idea how to what you are asking, but gallery2 uses a process of creating the user in gallery2 after you add a user in drupal, maybe there is some code there that can support the same process. http://drupal.org/project/gallery This module embeds Gallery2 (http://gallery.menalto.com) inside your Drupal installation to support photos, videos and other content. There is support for 2 types of image blocks and a navigation menu, inserting of images into nodes via an input filter, TinyMCE support, syncing of users between the 2 applications, ...
thanks this will come in handy. I guess I just want to know what api's to use to connect to ispconfig from drupal so that when the user in drupal is made a coresponding user in ispconfig is made etc. This way we can do it all in one place.