Which Interface to implement?

Hello, I’m trying to write an open-source plugin that will hash an incoming password using some algorith (SHA-512 for now) and then forward it to be compared from the OpenFire Engine, thus allowing to store hashed passwords in the database (not just plain text). I’m new to plugin development so I was wondering witch interface should I implement to capture the login (username and password) package?

Also if you know for some articles devoted on plugin development for openfire I will be very grateful