OAuth authentication with Facebook stopped to work

Site (www.lsdf.lv) unexpectedly stopped to authenticate with Facebook. It was happening years and then it returns (internally) a NULL from ExternalPartyCallback result. No code was changed in web app and also Facebook did not had any API updates at these days.
Running Web application locally on developmet machine authentication goes through no problems.
Could there be some restrictions put in place in WinHost networks?

 

It looks like Facebook dropped their API v2.2 support. Check out this Stack Overflow thread for a fix.