Let's say we have a piece of software which is licensed under the GPL. There are no binaries; it's a framework of groups of services and libraries of Python code running on a server.
As far as I can understand, private persons can modify GPL code and run it privately without having to disclose anything. They're not distributing anything.
But if a corporation/entity is using this software in question, or other libraries/software that simply runs on a server or in the "cloud" as a backend without distributing anything, do they need to disclose their modified source code?
The software in question here does let users interact with it through a web interface. You can also use a binary to communicate with the backend software through a CLI client program. Apart from that, everything takes place on a server.
The users of this software are not the public per se, but let's say for example students/employees at a college/university or similar.
The main question here is: Can the original authors of the software demand to see the modifications? Can the end users? If neither is true, what license other than the GPL would be appropriate? Would Affero GPL cover only the latter group, and not the former? Can the former group even be covered here?