Thanks for the answer!
I guess that could work for the native case, and then for the web case I might be able to get away with setting my github pages url as the redirect url and parsing document.location.search.
EDIT: after some research I think a custom protocol handler is a bit overkill for my needs, since I’ll only be using it for the login redirect.
Although since my app is a music player I might consider having a custom protocol to open songs directly in the native wrapper, that could be interesting.