AccessTokenRetriever getAccessTokenRetriever() {
        return accessTokenRetriever;
    }
@Test
    public void testConfigureWithAccessClientCredentials() {
        OAuthBearerLoginCallbackHandler handler = new OAuthBearerLoginCallbackHandler();
        Map<String, ?> configs = getSaslConfigs(SASL_OAUTHBEARER_TOKEN_ENDPOINT_URL, "http://www.example.com");
        Map<String, Object> jaasConfigs = new HashMap<>();
        jaasConfigs.put(CLIENT_ID_CONFIG, "an ID");
        jaasConfigs.put(CLIENT_SECRET_CONFIG, "a secret");
        configureHandler(handler, configs, jaasConfigs);
        assertInstanceOf(HttpAccessTokenRetriever.class, handler.getAccessTokenRetriever());
    }