The two options that an architect should recommend to UC are to build a custom web service that is supported by delegated authentication and to implement the OpenID protocol and configure an authentication provider. Delegated authentication is a feature that allows Salesforce to delegate user authentication to an external service instead of using Salesforce credentials3. A custom web service can be built to use the credentials stored in the custom identity store and validate them against Salesforce using SOAP or REST API3. OpenID is an open standard protocol that allows users to authenticate with various web services using an existing account4. An authentication provider can be configured in Salesforce to use OpenID and connect with the custom identity store5.