This module is a plugin for the SWI-Prolog HTTP/HTML framework to add reCAPTCHA functionality to a form. It works as follows:

1. Load library(http/recaptcha) and define the reCAPTCHA keys as described in key/2.
2. Create a form, typically using method('POST') and include, in addition to the data you request from the human user, the reCAPTCHA widget using e.g.,

   \recaptcha([theme(red)])

3. In the handler of the form, you must ask for the recaptcha parameters and pass them to recaptcha_verify/2. You can do that as follows:

   process_recaptcha_form(Request) :-
          recaptcha_parameters(RecapthaParams),
          http_parameters(Recaptha,
                          [ name(Name, []),
                            age(Age, []),
                            ...
                          | RecapthaParams
                          ]),
          (   recaptcha_verify(Request, RecapthaParams)
          ->  <process normal user fields>
          ;   <you are not human>
          ).

See also

- examples/demo.pl contains a fully functional demo.

 recaptcha(+Options)// is det

Display the reCAPTCHA widget. Defined options are:

theme(+Theme)

Set the theme. The default theme is clean.

See also

- https://developers.google.com/recaptcha/docs/customization describes the available themes

 recaptcha_parameters(-List) is det

List is a list of parameters for http_parameters/3 that is needed for recaptcha_verify/2.

 recaptcha_verify(+Request, +Parameters) is semidet

Is true if the user solved the captcha correctly. Fails if the user did not solve the captcha correctly but there was no error processing the request.

Errors

- recaptcha_error(Error) is raised if there was an error processing the captcha.

- domain_error(recaptcha_response, '') if the user did not fill out the captcha.

See also

- https://developers.google.com/recaptcha/docs/verify lists the errors.