> Does Solid mean we won’t need so many passwords?
> Yes. When you use Solid, you only need to login to your Identity Provider. You can then use applications that interact with your Pod without logging in each of them individually, which is (in our opinion) simpler than having to create accounts on each and every service. However, you will still have to manage what data you would like to share with each application.
Maybe I'm not understanding your direction here, but I'm specifically looking for an Identity Provider service to auth ActivityPub service users.