@joseph I believe it's a question of support still - as I'm trying to figure out to configure Cloudron's OpenID to work with external app, which Cloudron is about to repackage on it's own.
The link you've provided - is related to configuring Synapse server, while the issue is with Cloudron's OpenID and the way it handles redirect_uri
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Please, let me know if I shall not expect any reasonable and prompt support on that - if that is the case, I will have to replace the Cloudron functionality as a platform, and for that I will need quite some time.
I would be happy to work with someone from the team however, to keep Cloudron in my perimeter and share everything I will work on, so that you would be able to merge Synapse MAS and Element Call into the platform easily.