in the configuration, sets:
```
[forms]
captcha.recaptcha.validator = \jelix\forms\Captcha\ReCaptchaValidator
captcha.recaptcha.widgettype = recaptcha
[recaptcha]
;see https://developers.google.com/recaptcha/docs/display to know the meaning
; of these configuration parameters.
theme=..
type=..
size=..
tabindex=..
```
in the localconfig.ini.php, set the site key and the secret (see your google recpatcha account to retrieve them)
```
[recaptcha]
sitekey= your recaptcha key
secret= your secret value
```
then indicate to use recaptcha, in the <captcha> element or in the configuration
```
<captcha validator="recaptcha"/>
```
```
[forms]
captcha=recpatcha
```