Redmine

Hi,
I would need to do some (unrelated to Redmine) password synchronization on the same server whenever some user changes his/her password (or admin resets it, or whatever).
I'm not sure this is the right place to ask since I'm not a Ruby programmer.
Optimum (for me) would be to call some external executable (program or script) when:

• user is created
• password for user is created/modified

Is such a functionality available?
If not, can it be implemented easily?

Thanks in Advance
Mauro