plone.app.discussion/plone/app/discussion/browser/captcha.txt
Timo Stollenwerk af1a8bfacd Replace the old NOTES.txt and PRINCIPLES.txt with the Sphinx versions. Fix Captcha title.
svn path=/plone.app.discussion/trunk/; revision=36998
2010-06-04 11:22:16 +00:00

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Captcha Plugin Architecture
===========================
This document contains design notes for the plone.app.discussion Captcha plugin
architecture.
Introduction
------------
When a Captcha plugin (e.g. plone.formwidget.captcha or
plone.formwidget.recaptcha) is installed, plone.app.discussion
extends the comment form with a Captcha field/widget and a Captcha validator.
The form extender and validator are only registered if there is a plugin
installed that claims to provide the "plone.app.discussion-captcha" feature in
its configure.zcml file::
<configure ...
xmlns:meta="http://namespaces.zope.org/meta">
<!-- Declare that plone.formwidget.captcha provides a Captcha field that
can be used by plone.app.discussion to add a Captcha field to comment
forms. -->
<meta:provides feature="plone.app.discussion-captcha" />
...
</configure>
For an example see:
https://svn.plone.org/svn/plone/plone.formwidget.captcha/trunk/plone/formwidget/captcha/configure.zcml
Currently plone.formwidget.captcha and plone.formwidget.recaptcha provide such a
feature. If you want to write your own Captcha plugin, it has to provide this
feature as well.
CaptchaExtender
---------------
The CaptchaExtender class extends the comment form with a Captcha field and
widget. The CaptchaExtender currently uses either the CaptchaFieldWidget from
plone.formwidget.captcha or the ReCaptchaFieldWidget from
plone.formwidget.recaptcha. If you want to write your own Captcha solution, you
have to override the update() method of the CaptchaExtender or write your own
CaptchaExtender class.
CaptchaValidator
----------------
The CaptchaValidator class provides custom versions of the
plone.formwidget.captcha and the plone.formwidget.recaptcha validators. It does
this, because we want to be able to have more than one Captcha solution
installed in one Plone instance. We also want to be able to easily switch
between different Captcha implementations inside a single Plone instance.
Therefore we have to check which Captcha solution is enabled in the discussion
control panel and use only the selected Captcha validator. It is not enough to
check if a Captcha plugin is just installed, because there could be more than
one.
We do two checks. First we check for a suitable Captcha solution (check for the
plone.app.discussion-captcha feature, see notes above). Second, we check which
Captcha solution is enabled in the discussion control panel and apply the
corresponding field validator.