Our apps are getting error 500 on this call :
https://www.facebook.com/dialog/oauth?client_id=89dc1edc0036d868930ccbac657e8b7f&redirect_uri=https%3A%2F%2Fapps.fa
Facebook seems to have dropped support for the old API KEYs. If you look at your App Settings page, you'll see App Id/Api Key. These were merged back in 2011, so just replace your api_key with your app_id for the client_id parameter.
This should have been a breaking change.