Just found one workaround to login Chat Mac App: Just change all the 'IN_NEW_WINDOW' and "EXTERNAL" to "_blank" in /Applications/Chat.app/Contents/Resources/app/main.js. Then start the Chat App and login, you can use the Chat App now.
And this should work on the latest Chat App. Not sure if the older version works.
Sorry, just found some issues when I do the changes on another employee's laptop. Not to replace all. I just open it with sublime and http prettify it. Then change 'IN_NEW_WINDOW' and "EXTERNAL" to "_blank" on line 2858, 2865 and 3058. And the related function names in my file are "b.va = function(a, c)" and "var ue = function(a, c, d, e, f, g)"
@xfkwang Huh, that's impressive.