How is the “signup cta” sign up URL set?

¿ Is this really how it’s supposed to work. ?

I mean, how does it know at all what to link that ‘Sign up’ button to?

…it seems hard to believe the Discourse would just, “let’s just link ‘sign-up’ to the same place as ‘sign-in’…” How is this not annoying/broken for everyone using SSO.