I wonder if you're trying to do too much with the RPT token. Remember, RPT is backchannel (i.e. the UMA token endpoint). You would have more flexibility interacting with the end user if you used the claims gathering flow, which has it's own script. You don't need SCIM, because in oxAuth you can connect to the underlying database. You only need a SCIM extension for UMA resources if you have a third party application that needs to manage UMA resources for the person. If you want to schedule a call to whiteboard, we can try to help you think this through. I would also suggest that you create a sequence diagram using https://sequencediagram.org and post the source here. Without a sequence diagram, it's really impossible to know that you have consensus on a solution.
BTW, UMA has tepid adoption, so the support team is not well versed in configuration and customization of these flows. I'll take over this issue for now. But so you are fore warned, it's a little outside the scope of community support.