Custom OpenID Connector?

We are using Onelogin as our SSO ID and need a private forum solution that we can force login through Onelogin and two-factor authentication. Unfortunately because Vanilla won't add SAML to the open source version, that option is out. Onelogin does support OpenID; however, the only OpenID support for Vanilla seems to be social. Is there a open source plugin that can be used for this (or at least modified to our liking - i'm a programmer, just not great at PHP) so we can integrate OpenID connect to Onelogin? I've exhausted pretty much every other avenue I can find, and unfortunately it seems like no self-hosted forum software seems to be keen on making SSO easy.
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There is an OpenID Pugin and the steam connect is using OpenID too (not 100% sure about the steam plugin)
https://github.com/vanilla/vanilla/tree/release/2.6/plugins/OpenID
https://github.com/vanilla/addons/tree/master/plugins/SteamConnect
Do they not provide an OAuth2 option? That’s what I’d want to go with. We do have support for that in open source.