The update User() methodonthe Registration Handler class is used to update the Salesforce user record with information from the Facebook profile, such as name, email, and photo1. This method is invoked every time a user logs in to Salesforce using Facebook credentials2. The other options are not suitable for this requirement because:
* SAML Just-In-Time Provisioning is used to create or update users in Salesforce based on SAML assertions from an identity provider3. Facebook does not support SAML as an identity provider.
* The Signed Request is a parameter that contains information about the user who is logging in to Salesforce via Facebook. It does not contain the user's profile information, such as name, email, or photo.
* A scheduled job that calls out to Facebook on a nightly basis would not reflect the changes in the Facebook profile in real time, as the requirement states. It would also require storing the user's Facebook access token and making API calls to Facebook,which could be inefficient and insecure.
References: Set Up Social Sign-On, Configure a Facebook Authentication Provider, SAML Just-in- Time Provisioning, [Facebookas a SAML Identity Provider], [Facebook Login for Apps - Signed Request], [Facebook Login for Apps - Access Tokens], [Facebook Graph API - User]