What is the role of Salesforce in the context of SSO, based on this scenario?

Containers (UC) uses a legacy Employee portal for their employees to collaborate. Employees access the portal from their company’s internal website via SSO. It is set up to work with SiteMinder and Active Directory. The Employee portal has features to support posing ideas. UC decides to use Salesforce Ideas for voting and better tracking purposes. To avoid provisioning users on Salesforce, UC decides to integrate Employee portal ideas with Salesforce idea through the API.

What is the role of Salesforce in the context of SSO, based on this scenario?
A . Service Provider, because Salesforce is the application for managing ideas.
B. Connected App, because Salesforce is connected with Employee portal via API.
C. Identity Provider, because the API calls are authenticated by Salesforce.
D. An independent system, because Salesforce is not part of the SSO setup.

Answer: D