Using OWIN 4.0.1 on my sites – the google authentication worked fine but I couldn’t find out why the Facebook process always returned null – redirecting only to the same URL – adding the typical #_=_ to the /Account url. Finally thought of my Cloudeflare proxy and that it might be impacting Facebook’s response. Turning off the cache solved the issue – but maaaaan how much I have learned in the past 10+ hours spent on this 😉 #liveandlearn