Hi Paul,
Please correct me if I am wrong. I believe with "oxauth-rp", you are mentioning our test site "seed.gluu.org/oxauth-rp".
If that is so, I am sorry to inform you that it's not actually a good idea to use this site for your client registration because it's kind of back dated and we are not giving too much effort on this test site as we will decommission it very soon.
We have a plan to integrate this client registration as native app in our future CE release.
Till then, I would request you to use your own client registration API if you find anything interesting.
Please feel free to let us know what you think; we are open to share knowledge.
Kind regards,
Zico