Set username on registration as firstname+user id

This is my scenario:

NO username required on registration form;
I use also CB Connect to let user create account;
I don't want that username is setted as e-mail for privacy reasons;
If 2 users have the same first and last name then the username "first name last name" can be taken only by 1 person and that's annoying expecially in cases where users connect with Facebook plugin.

I would create an auto action that edit the username as soon as the user is created as: [name][user_id]

I've tryed it and partially worked: setted "onAfterSaveUserRegistration" and in case the user register from the CB form everything works fine but if user registers using CB connect (FB for example) the trigger is not fired.

Also, in the email that the user receive I would have the username as [name][user_id].

How could I do that?

First solution found myself:

I've setted the CB Connect plugin for Facebook to assign as username the Facebook ID. In this scenario, if user register via CB, then the auto action assign the username as firstname-user_id, meanwhile if user registers via Facebook the username is assigned as facebook_id and autoaction is bypassed.

Anyway, is there another way to set the username as "firstname-userid" in case that user registers with Facebook Connect?

Yes, within CB Connect > Parameters > Registration you can use the "Username Format" parameter to format the username however you like. Additionally supported substitutions are listed below the parameter. So in your case you'd set it as follows most likely.

[profile_firstname]-[facebook_id]

If that doesn't grab the firstname you can try the below.

[firstname]-[facebook_id]