I’ve succesfully connected OpenFire to AD and can log into via Spark with my AD account. Is there a way to pass the login credentials already used?
That is called SSO authentication. This document will get you started: http://www.igniterealtime.org/community/docs/DOC-1060. Please also post specifics about you configuration if you have problems with this process (server OS, server version, client version, client OS).