Hello 
I’ve started yesterday new thread - Push Notifications (Push API) - to get feedback on how people envision such features where need to run ‘somewhere in the cloud’. Thinking that solid servers like NSS should stay generic, I would imagine writing some kind of bot that would take such custom responsibility. Any app that can run on someone’s device could also have component that runs in a cloud as a bot service.
Services implemented as such bots could already use Solid Websockets API and build their functionality around that subscription. AFAIK @codenamedmitri did most of the work on WebID-OIDC and maybe could share some insights on best practices for having such services (aka bots) authenticated.
I also see need that as Progressive Web Apps get traction and more and more people will run Solid apps on their mobile devices, sometimes to optimise for battery usage and mobile data usage applications will need to offload some work to server side components running ‘in the cloud’, I think twinql agent could come as one of possible examples: https://dan-f.me/twinql/
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Cheers!