@SuppressWarnings("unchecked")
    @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));
        if (Objects.requireNonNull(jaasConfigEntries).size() != 1 || jaasConfigEntries.get(0) == null)
            throw new IllegalArgumentException(
                    String.format("Must supply exactly 1 non-null JAAS mechanism configuration (size was %d)",
                            jaasConfigEntries.size()));
        this.moduleOptions = Collections
                .unmodifiableMap((Map<String, String>) jaasConfigEntries.get(0).getOptions());
        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/unsecured/OAuthBearerUnsecuredValidatorCallbackHandler.java