Re-reading your question, my definition of “integrate” was a bit simpler than yours.
Does that mean that the person in the Discussion doesn’t have an account in Salesforce? That does seem complicated, though the [DEPRECATED] The Github Linkback Plugin might be a starting place to solve that.
That much is true!
I’m not clear exactly what you’re trying to accomplish (I probably don’t know enough about Salesforce enough to understand the question).