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you have to edit openvpn.conf.

add something like that :
management 127.0.0.1 portyouwant /path/to/filecontainingpassword
create the password file, write your password on the first line, fix acl with access only for openvpn usr
restart openvpn
go to openvpn plugin in ajenti, fill the form with adress:port and the password defined in the fill
restart ajenti
enjoy, you can see who is connected, and log, I don't know if it's possible to create or modify an openvpn profile.