Clef have announced that they are sunsetting their secure login service, the service will cease to work on 6 June 2017.
The sunsetting and closure was announced on the Clef Blog, but no reason for the decision was given.
Clef was one of, if not the best, login service I had found for the many WordPress websites I manage. It took away the pain of managing multiple usernames and passwords, and it was incredibly cool. Clients used to love the login magic of Clef.
I hope that more information will come out over the coming weeks and maybe Clef will live on in some form or other. In the meantime I'm going to be revisiting and reviewing other 2FA services to see which one is the best for me to use across my sites.