Select in Genenral Settings: Allow external users to sign up. Then go to Oauth Providers. Select Facebook. Then go to : https://developers.facebook.com/apps  Register there. Get needed Credentials and then it Works!

Hi ,

Hope this is not too late , for the answer , but as it is for v10 community, hope it helps .

i have wrote a complete guide / tutorial with facebook login for Odoo , with screen shots on how to get the client-id from facebook developer here , please take a look 

http://blog.instant-erp.com/2017/03/how-to-setup-sign-in-using-facebook-to.html

Hope that is helpful , 

regards,

Kalmen

Instant-erp