Hi @adam.housman!
First of all, thank you for the very quick reply! 
It could well be that my concept has flaws already, so let me quickly describe my use-case:
I have an application which offers online-courses which will be provided by different partner organizations. I have an SPA for the end-user frontend and one for the admin-interface. The database is handled via Dgraph which basically acts as an API gateway.
Since the partner organizations will have their own skinning, my app fetches the domain (multiple domains point to the same SPA), and renders accordingly so the user experience is that of an “individual application” of the organization.
This works quite well and fortunately I need a user authentication for the different users for the different organizations. Auth0 has been selected to be the weapon of choice - which does work pretty nice so far. With different login skins I have a customised user exoirence for logins but unfortunately users will also have to sign up at one point. I have found that if I set the end user access in the application settings to both, users can sign up again but unfortunately the signup is not customised. Even worse, after the signup users will get redirected to the destination of the organization they have signed up from but obviously they aren’t “officially” part of the organization yet, since this would require another login (assuming auto-membership is enabled for the connection in the organization settings).
I guess I could write my own login and signup screens but then I would also need to fiddle around with social logins etc. - all of which is included in your interface already.
Is that a valid use-case? Am I missing something?
Thanks!