Full code is available on the plugin page: [[plugins/contrib/justlogin]].
I searched the site and there's very little info available for postsignin or redirect. Perhaps I'm using the wrong function?
+
+> I don't know why you end up on the prefs page. Have you tried
+> looking inside the session database to see what postsignin
+> parameter is stored?
+>
+> But, `cgi_postsignin()` assumes it can directly pass the postsignin cgi
+> parameter into `cgi()`. You're expecting it to redirect to an url, and it
+> just doesn't do that. Although I have considered adding a redirect
+> there, just so that openid login info doesn't appear in the url after
+> signin (which breaks eg, reload). That would likely still not make your
+> code work, since the value of postsignin is a url query string, not a
+> full url.
+>
+> I'd suggest you put a do=goto redirect into postsignin. --[[Joey]]