How the login details to a Genius Hub work
Each Genius Hub has a single username and password. These need to be set to something that the owner of the system is happy to give to anyone they want to be able to control the heating.
What if two people are logged in at the same time?
If two people are logged in at the same time, this is fine. If conflicting actions are taken (such as two overrides being selected), the Genius Hub will act on the last command it receives from any of the apps logged into it.