public boolean isValid(Instant instant) {
        final Instant expires = expiresAt();
        return (expires == null) || requireNonNull(instant, "instant").isBefore(expires);
    }
Indicates whether or not the Access Token expire at the given {@link Instant} time based on
{@link #expiresAt()} function.
oauth2/src/main/java/com/linecorp/armeria/common/auth/oauth2/GrantedOAuth2AccessToken.java