I mean, it just sounds like the people from your Tools/Infrastructure/IT/Devops/whatever-it's-called-for-you department are fucking incompetent and can't properly configure a Single Sign-On. Took mine a few years as well, I think the ticket was stuck in the queue behind the "restart some servers when nobody's watching to see how long until they find the issue" tickets, which they seemed to be working on weekly.

Also, I can't think of any reason why SSO can't work with Mozilla or Chrome also, not just with Edge.