private SaslExtensions saslExtensions() {
        return SaslExtensions.empty();
    }
We don't want to use mocks for our tests as we need to make sure to test
{@link SaslExtensions}' {@link SaslExtensions#equals(Object)} and
{@link SaslExtensions#hashCode()} methods.

<p/>

We need to make distinct calls to this method (vs. caching the result and reusing it
multiple times) because we need to ensure the {@link SaslExtensions} instances are unique.
This properly mimics the behavior that is used during the token refresh logic.

@return Unique, newly-created {@link SaslExtensions} instance
clients/src/test/java/org/apache/kafka/common/security/oauthbearer/OAuthBearerLoginModuleTest.java