Universal containers (UC) has a customer Community that uses Facebook for authentication.

 Using information in the signed request that is received from Facebook is how this requirement can be met. A signed request is a parameter that contains information about the user who is logging in with Facebook credentials. The signed request can include information such as the user ID, name, email, and profile picture. You can use this information to update the corresponding customer community user in Salesforce by implementing a registration handler class. The registration handler class is an Apex class that defines how Salesforce handles user registrationand authentication when using an auth provider. You can use the updateUser() method in the registration handler class to update the user record with the information from the signed request. Using the updateUser() method on the registration handler class isnot how this requirement can be met because it is only part of the solution. You also need to use information from the signed request as the source of the updates. Using SAML just-in-time provisioning between Facebook and Salesforce is not how this requirement can be met because Facebook does not support SAML as an identity provider protocol. Developing a scheduled job that calls out to Facebook on a nightly basis is not how this requirement can be met because it is inefficient and unnecessary. You can update the user record in real time using the signed request instead of waiting for a nightly batch process.