For the AuthManager integration in SUL3 (T348388: Use central login wiki for login (SUL3)), we'll use a REDIRECT response in the local wiki that sends them to the login form on the central wiki. To make that smooth, we need to meet the conditions in LoginSignupSpecialPage::canBypassForm() so that the user is not shown a pointless interstitial page on the local wiki, ie. no authentication provider (other than the CentralAuth primary provider doing the redirect) should return an AuthenticationRequest from getAuthenticationRequests( ACTION_LOGIN ), unless it is marked skippable. Chances are this is already the case, but we'll need to review authentication extensions used on Wikimedia wikis to make sure.