Thread:Extension talk:Phpbb Single Sign-On/Using Special:UserLogon and Special:UserLogout in liue of skins modifications/reply (4)

The suggestion above is definitely a better approach, rather than modifying the various skins.

Also, I found some system messages weren't using forum login links, on my 1.19 MW instance. I ended up modifying the system messages MediaWiki:Whitelistedittext and MediaWiki:Loginreqpagetext (and actually hardcoding the login link in them, which felt like a bad hack). But it works! :)