@SuppressWarnings("unchecked")
    public final T refreshBefore(Duration refreshBefore) {
        delegate.refreshBefore(refreshBefore);
        return (T) this;
    }
A period when the token should be refreshed proactively prior to its expiry.
oauth2/src/main/java/com/linecorp/armeria/client/auth/oauth2/AbstractOAuth2AuthorizationGrantBuilder.java