String identity = PartakeApp.getOpenIDService().getIdentifier(receivingURL, params, discoveryInformation);
        if (identity == null)
            return renderRedirect("/", MessageCode.MESSAGE_OPENID_LOGIN_FAILURE);
        // TODO: UserEx が identifier から取れるべき
        UserEx user = new GetUserFromOpenIDIdentifierTransaction(identity).execute();
        if (user != null) {
            session().put(Constants.Session.USER_ID_KEY, user.getId());
            if (getRedirectURL() == null)
                return renderRedirect("/");
            else
                return renderRedirect(getRedirectURL());
        } else {