One could pull LDAP and push it into PostgreSQL periodically. This would be the ultimate form of integration as it would allow the most freedom and have accentual usage cases. Adding an *API from managing the user database as well as nagios config is something we have considered.
* This would consist of a URL that is not state-full(I.E. no cookies). The idea of using XML as a container was suggested, though for our usage it'll most likely be regular post data. To use XML the examples I've seen convert the XML into a file and base64 it pushing it as a normal post data/file upload.