Filter for web integration of the CaptchaServiceProxy .
It basically intercept calls containing the specific validation parameter, use the CaptchaServiceProxy to validate the request, and update the CaptchaSecurityContext if the request passed the validation.
This Filter should be placed after the ContextIntegration filter and before the CaptchaChannelProcessorTemplate filter in the filter stack in order to update the CaptchaSecurityContext before the humanity verification routine occurs.
This filter should only be used in conjunction with the CaptchaSecurityContext