How to use Help center users (frontend users) as SSO provider

How to use Help center users (frontend users) as SSO provider

I want to implement something like the SAML option in Zoho Desk, but backwards - I want to use the Help center (frontend) users in Zoho to log them in to another system - thus my Zoho portal would be the identity provider and the other system would be the service.

My current use case is a self-hosted Nextcloud, which supports SAML 2, but we would integrate more systems in the future.

Does anyone know a way to do this?

Of course we have the alternative to create our own user management and use that as the identity provider, but we already have a lot of users in our Zoho portal and we don't want to change the way they login.
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