We have a PHP based web application with a lot of project data. All of our customers have a dedicated instance of this application.
Now we want to allow a very limited access to some third party users to access some data (read only). We want to create a new dedicated app for these read only users and allow each our customers - with the main app - to select what to share. The communication is REST based.
So we need to create a user entity in each systems. For example John Doe can login in the read only app and our customer want to set what John Doe can see in the base app. Facebook, Google logins are not allowed.
My question is what is the best way to link / connect these 2 users?
To be more precise. The readonly user can log in only into the new and limited application and he/she never allowed to login to the main app. So the readonly user has a real user entity in the readonly app only.
However we need some representation of the readonly user in the main app as well to allow the main app admin to share data.
Every time a readonly user logs in to the readonly app we always ask for the shared data in the main app with a REST call.