Explanation
The two recommended actions UC can take to achieve the functionality of allowing community users to register and log in with LinkedIn or Facebook credentials are:
Enable Facebook and LinkedIn as login options in the login section of the community configuration.
This action allows UC to configure Facebook and LinkedIn as authorization providers in Salesforce, which are external services that authenticate users and provide information about their identity and attributes. By enabling these login options in the community configuration, UC can display Facebook and LinkedIn icons on the community login page and allow users to log in with their existing credentials from these services.
Create custom registration handlers to link LinkedIn and Facebook accounts to user records. This action allows UC to create Apex classes that implement the Auth.RegistrationHandler interface and define the logic for creating or updating user accounts in Salesforce when users log in with LinkedIn or Facebook.
By creating custom registration handlers, UC can map the information from the authorization providers to the user fields in Salesforce, such as name, email, profile, or contact.
The other options are not recommended actions for this scenario. Storing the LinkedIn or Facebook user IDs in the Federation ID field on the Salesforce user record is not necessary or sufficient for enabling SSO with these services, as the Federation ID is used for SAML-based SSO, not OAuth-based SSO. Creating custom buttons for Facebook and LinkedIn using JavaScript/CSS on a custom Visualforce page is not advisable, as it would require custom code and UI development, which could increase complexity and maintenance efforts.
Moreover, it would not leverage the built-in functionality of authorization providers and registration handlers that Salesforce provides. References: [Authorization Providers], [Enable Social Sign-On for Your Community], [Create a Registration Handler Class], [Auth.RegistrationHandler Interface], [Federation ID]