Handle service ticket validation on proxyValidate endpoint, return error on proxy endpoint

 src/main/java/org/keycloak/protocol/cas/CASLoginProtocolService.java

@@ -69,12 +69,13 @@

    @Path("proxyValidate")
    public Object proxyValidate() {
        return null;
        //TODO implement
        return serviceValidate();
    }

    @Path("proxy")
    public Object proxy() {
        return null;
        return Response.serverError().entity("Not implemented").build();
    }

    @Path("p3/serviceValidate")