[keycloak-dev] Captcha on Login Page

Hello, I have recently been tasked with enhancing our Keycloak 2.5.1 login page with ReCaptcha functionality. We currently are planning to use the default login page, and were originally under the impression that fields could be added to it using a FormAction provider. It appears that login page is not compatible with the FormAction provider, though. Various comments, including those on https://issues.jboss.org/browse/KEYCLOAK-4379 , have noted that the Authentication SPI should be used instead. The problem I am running into is that it appears the Authentication SPI is only for adding new pages to the login flow; it does not appear to support modifying the existing login page, unless I'm missing something. Is there a way to modify the existing login page and logic such that no attempts will be made to log the user in unless he enters the correct captcha, similar to the way ReCaptcha is implemented in the registration flow? Thank you for your help, David Lustig