[keycloak-user] custom authenticator invoking with a REST API for authentication

Hi, We have a need to intercept the existing form based login authentication for a realm and instead of going to the Keycloak database to validate username/password we need to invoke a REST endpoint with the username/password combination to authenticate the user. Using the User Storage SPI is not an option since it integrates at the JPA layer. We will need to integrate via an authentication REST API hosted externally to RH-SSO.  Please provide some of the options that are available to us to accomplish. Appreciate the help. -sud