To activate this option for your domain, follow the steps below:
1. Go to the Account & settings->Users tab (1) and allow the direct signup of the users (2).
2.Click on the Social media link (3) to reveal the available options. Select the setting Allow signups through social media and then select those you want to use (4).
From now on there will be a link in your portal's home page that will prompt the users to login through Facebook, Linkedin or Google (5):
Note: Login through Facebook does now work on mapped domains.