Validating in behavior (recapcha)

I am making a behavior for
(If there is already an add-on for this, let me know).

Since the plan is to make this a behavior: how do can I validate the field?

The google docs refers to 'submitting of the form', but do I have 'access to that from the behavior' ?

When your users submit the form where you integrated reCAPTCHA, you'll 
get as part of the payload a string with the name 
"g-recaptcha-response". In order to check whether Google has verified 
that user, send a POST request with these parameters:URL: (required)6Le8IgsUAAAAAChoJrpvyraPt2oJcqDQtmTZxnOPresponse (required)The value of 'g-recaptcha-response'.remoteipThe end user's ip address.The reCAPTCHA documentation site describes more details and advanced configurations.

... I am putting the code here:

I would add it to collective.recaptcha instead of making it an own package.

Also plone.formwidget.recaptcha is a thing if it comes to z3cform

Is this add-on "basically doing the same" ?
I have tried (without luck) to use it (also the github version)

it basically provides recaptcha support. it does not provide a field/widget. The widget is provided by plone.formwidget.recaptcha. So it should need just a bit glue code and minor bits of logic to provide a behavior.

Could you please elaborate on these bits of glue code and logic?

I am currently trying to implement a v2-recaptcha in the plone 4.3.3 member self-registry and it turned out to be a major headache. How can i add anything to @@register oder @@register-confirm-email? When added with TAL in a customized view the recaptcha is working - but how can i add it to @@register?
All i found in forums were instructions about some python files, but i lack the basic knowledge of where to begin. Is there any way to achieve this in zope?

So far i tried with collective.recaptcha, collective.registrationcaptcha, plone.formwidget.recaptcha and collective.emailconfirmationregistration, but i can't find any view or option for @@register anywhere.

Edit: i opened a new thread for this question