public boolean isNotBefore() {
        final Instant notBefore = notBefore();
        return (notBefore == null) || Instant.now().isAfter(notBefore);
    }
Indicates whether or not the Token used prematurely based on {@link #notBefore()} function.
oauth2/src/main/java/com/linecorp/armeria/common/auth/oauth2/OAuth2TokenDescriptor.java