Available facebook module for Drupal 8:
Facebook Share: http://drupal.org/project/facebookshare Allows users to share a Drupal node on Facebook. Similar to the new "Universal Like" widget from Facebook. NOTE: This module has been tested to work in Chrome 4+, Safari 4+, Firefox 3.5+, IE 7+, and Opera 10.5+ on Windows (Chrome, Safari, Firefox, IE, and Oper), Mac OS X (Chrome, Safari, and Firefox), and Linux (Chrome and Firefox). If it is not displaying on your website and your theme uses PHPEngine, be sure to include print $closure; just before the </body> tag.
Simple FB Connect: http://drupal.org/project/simple_fb_connect Simple Module providing FB login/registration. Profile pic can be synced during registration. Provides Rules events so that you can extend functionality. Provides an API for other modules for extending Facebook integrations. Well documented. Module version 2.x uses Facebook PHP SDK v4.0, which is using Facebook API v2.3.
Installation instructions and module handbook
Note: Version 8.x-3.x MUST be installed using Composer as documented on the installation instructions. The .zip and .tar.gz files below are only for informational purposes. The module can NOT be installed directly from them.
Full read on this source: https://groups.drupal.org/node/65268