@Override
    public void configure(Map<String, ?> configs, String saslMechanism, List<AppConfigurationEntry> jaasConfigEntries) {
        if (!OAuthBearerLoginModule.OAUTHBEARER_MECHANISM.equals(saslMechanism))
            throw new IllegalArgumentException(String.format("Unexpected SASL mechanism: %s", saslMechanism));
        configured = true;
    }
Return true if this instance has been configured, otherwise false

@return true if this instance has been configured, otherwise false
clients/src/main/java/org/apache/kafka/common/security/oauthbearer/internals/OAuthBearerSaslClientCallbackHandler.java