Hi Wim,
I don't know of any software or plugs in myself but among the first places I search to benchmark for different types of software is Capterra https://www.capterra.com/proctoring-software/
This software is pretty standard now so more established suppliers should have off the shelf integrations which could be adapted?
An alternative approach - previously recommended by a developer - was to look at what had been adapted to work with Moodle given codebase overlap and see if that could be further adapted.
Hope that helps