fix backchannel 2
implement RP-initiated logout to Keycloak On WP logout, redirect to Keycloak end_session_endpoint with id_token_hint so the Keycloak session is also terminated. Store id_token in PHP session during login callback. Fall back to home_url() if endpoint is unavailable. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>