Explanation
User Interface API should be used to implement this integration. User Interface API is a RESTful API that allows you to create native mobile apps and custom web apps with the look and feel of Salesforce's Lightning Experience. User Interface API provides access to metadata, data, and UI components, such as layouts, actions, picklists, and record types. User Interface API also handles security, performance, and compatibility across different devices and browsers. References: Certification - Integration Architect - Trailhead, [User Interface API Developer Guide]

Explanation
OpenId Connect Authentication Provider and Registration Handler, and SAML SSO and just-in-time provisioning are two requirements that the Salesforce Community Cloud can support for self-registration and SSO. OpenId Connect is a protocol that allows users to authenticate with an external identity provider and access Salesforce resources. A registration handler is a class that implements the Auth.RegistrationHandler interface and defines the logic for creating or updating a user in Salesforce after authentication. SAML SSO is a protocol that allows users to log in to Salesforce with a single click, using an assertion from an identity provider that confirms the user's identity. Just-in-time provisioning is a feature that allows Salesforce to create or update a user account based on the information in the SAML assertion. References: Certification - Integration Architect - Trailhead, [OpenID Connect Authentication Providers], [SAML Single Sign-On (SSO) Service for Salesforce]

Explanation
Remote Site Settings and Named Credentials are solutions that should be implemented to minimize potential downtime for users in this situation. Remote Site Settings allow you to specify external domains that your organization can access during API calls or integrations. Named Credentials allow you to store authentication information for external services in a secure way. By using Named Credentials, you can easily update the URL of the external service without changing any code or configuration that references it. Enterprise Service Bus (ESB) and Remote Site Settings are not solutions that should be implemented in this situation because ESB is a middleware that facilitates communication between different systems, not a way to update the URL of an external service. Event Monitoring and Content Security Policies are also not solutions that should be implemented in this situation because Event Monitoring is used to track user activity and performance metrics, not to monitor external service availability. Content Security Policies are used to control what resources can be loaded on a web page, not to update the URL of an external service.