in our project, all the data from multiple devices are collected in a single point (MQTT broker) and from there, an automated process should put the values into OpenRemote in multiple realms. I could not find a way to have a service user that can put values in multiple realms (and can also create new assets in hundreds of realms).
It does not make sense to create service users in every realm and to connect to every realm with a separate service user. It is a huge overhead in our case.
Is there a way to log in with master:admin as a service user?
Please advise on the possibilities to create realms and assets in different realms and populate the assets with values through the API. can be REST, websockets, MQTT or whatever.
From an authentication perspective realms are completely isolated from each other so users cannot generally work across realms with the exception of super users (users in the master realm with admin realm role).
You could configure a service user as a super user but consider the risk if this user is compromised.
Alternatively you can write a custom MQTT handler which would run in the backend as a trusted code and can freely commit data in any realm.