The Facebook SSO Addon written for WHMCS has been verified on the new v7.1.x WHMCS and it still works as advertised.

Going forward we will be working on a more diverse Addon which will take advantage of a few more SSO providers and we hope to bring this to market within the first quarter of 2017.

We are also waiting out on approval from WHMCS Marketplace for the listing to be published. Our previous attempt had the wrong compatibility data added so our listing was denied (hopefully this will be rectified soon).

MTFBWHMCS has been officially completed and is available for introductory implementation in your WHMCS implementations.

Once implemented, site operators will be able to accept Facebook logins and registration by customers seamlessly.

See more here