SSO has nothing in particular to do with two-step login.
Two-step login is just a way of getting a branded experience in front of the user as soon as possible, nothing more. It is neither necessary nor indicative of SSO (which you have described correctly.)
>Two-step login is just a way of getting a branded experience in front of the user as soon as possible, nothing more. It is neither necessary nor indicative of SSO (which you have described correctly.)
That might be part of it, but the real point is companies do not want others to MITM their user's passwords.
