@Test
    public void unrecognizedExtensionsAreNotSaved() throws Exception {
        saslServer = new OAuthBearerSaslServer(EXTENSIONS_VALIDATOR_CALLBACK_HANDLER);
        Map<String, String> customExtensions = new HashMap<>();
        customExtensions.put("firstKey", "value1");
        customExtensions.put("secondKey", "value1");
        customExtensions.put("thirdKey", "value1");

        byte[] nextChallenge = saslServer
                .evaluateResponse(clientInitialResponse(null, false, customExtensions));

        assertEquals(0, nextChallenge.length, "Next challenge is not empty");
        assertNull(saslServer.getNegotiatedProperty("thirdKey"), "Extensions not recognized by the server must be ignored");
    }
SASL Extensions that were not recognized (neither validated nor invalidated)
by the callback handler must not be accessible through the {@code #getNegotiatedProperty()} method
clients/src/test/java/org/apache/kafka/common/security/oauthbearer/internals/OAuthBearerSaslServerTest.java