hi!
So what you need is Single Sign On from Ghost into Discourse, right?
It doesn’t look like Ghost supports being an ID Provider. If it did, you could seamlessly integrate your Ghost user accounts with Discourse accounts.
The next best option would be for Ghost to support OAuth2 login (ie. be a resource provider, in SSO parlance), so that accounts could live on a separate ID provider service to which both Ghost and Discourse would integrate via OAuth2.
But Ghost does not support OAuth2 yet, though there’s hints of plans to support OAuth2 authentication here:
The last post in that topic links to the only open source SSO solution for Ghost I could find on Google, but in turn, it says:
NOTE: development in progress. Do not use it!
note: there is this AuthDigital service which claims to integrate to Ghost (not sure how), and it also supports Discourse SSO, so in theory this could be that separate ID provider for both your Ghost and Discourse sites: https://authdigital.com/ghost-single-sign-on
That said, we have no experience with them so we can’t vouch for them; also, no mention of them on Meta. Up to you.