@Override
    public String toString() {
        return "LoginManager(serviceName=" + serviceName() +
                // subject.toString() exposes private credentials, so we can't use it
                ", publicCredentials=" + subject().getPublicCredentials() +
                ", refCount=" + refCount + ')';
    }
Decrease the reference count for this instance and release resources if it reaches 0.
clients/src/main/java/org/apache/kafka/common/security/authenticator/LoginManager.java