Starting with Sytist version 1.2 is the ability to have your customers login with their Facebook account.
When they use that option, it will capture their first name, last name and email address*. If their email address is the same as an existing account, it will log them into that account. If the email address is not part of an existing account, then it will create them a new account and log them in.
* it is possible that it will not capture their email address. This can be caused by the person creating their Facebook account with their phone number or have elected not to share their email address.
To enable this option, in your Sytist admin go to Settings -> Share & Facebook. You will have an option to enable it. You will also have to create a Facebook APP if you haven't already and enter in the APP ID and APP Secret. Here is how to get your Facebook APP ID.
After you have enabled this option and added your Facebook APP ID and APP Secret, you should test it out yourself to make sure it is working properly. To do so, go to the front end of your Sytist site and choose to log in or create an account (If you are already logged into a customer account, log out). Then select the login with Facebook option.