Continuing the discussion from Official Single-Sign-On for Discourse:
If you require users to be logged in to view your page, and you have SSO enabled, they will be logged in automatically (no splash page).
As @codinghorror mentioned, if you want to change the behavior you can add this as an admin option into a PR.
@wesochuck, how do users log in on your forum already?
Do they go to a specific website then click “forum”?