@Hikerd – if you’re still thinking about writing your own JS-based app, i wanted to let you know that I tried to make a simple single-page web app that uses PKCE OAuth flow and the iNat v1 API, and i’ve confirmed that it is possible to do that.
example: https://jumear.github.io/stirfry/iNat_PKCE_flow_example.html (doesn’t work in Edge / IE)
code: https://github.com/jumear/stirfry/blob/gh-pages/iNat_PKCE_flow_example.html
I’m still not sure the API provides the capabilities to do what you were describing in your original post, but if it does, JS should allow you to achieve what you were describing.