An IdP (Identity Provider) server is responsible for authenticating user credentials. It verifies the identity of a user by handling the authentication process and often provides identity information to service providers in the form of security tokens or assertions. The primary function of an IdP is to authenticate users and then communicate that authenticated identity to other systems or applications.

To allow a remote Cisco Jabber user utilizing Mobile and Remote Access (MRA) to automatically log in to a Cisco Unity Connection voicemail box via OAuth, it is necessary to add CUCM under System Settings > Authz Servers in Cisco Unity Connection. By configuring this, the OAuth tokens needed for authentication can be managed and validated properly, ensuring seamless and secure access to voicemail services.

The issue is caused because the Voice Mail Pilot is not configured with a CSS that contains the INTERNAL_PT. The Voice Mail Pilot needs a Calling Search Space (CSS) that includes the partition of the Hunt Pilot to properly forward calls to voicemail. In this configuration, the Voice Mail Pilot is using the default CSS, which likely means it cannot reach the INTERNAL_PT partition, causing the calls to fail when forwarded to voicemail.

The error message indicates a failure in switching mode to a device due to an issue with opening the device. The suitable end-user setting here would be to allow control of devices supporting rollover mode, which can help in managing device switching and control issues, resolving the problem indicated in the error message. Therefore, the correct answer is 'Standard CTI Allow Control of Phones Supporting Rollover Mode'.

When a high availability event takes place in the Cisco IM and Presence solution, the end user sessions are transferred from the failed server to the backup server to ensure continuous service. This mechanism helps maintain session continuity and prevents disruption for the end users.