A company is deploying a new instant messaging app to allow for communications with external vendors. Each entity will host its own version of the application, but users must be able to talk between t

User synchronization involves copying user accounts between directories, which is complex and does not inherently provide the real-time, cross-domain communication required for federated instant messaging.

Password synchronization only ensures consistent passwords across systems but does not address the fundamental need for cross-domain identity trust and communication between disparate application instances.

Public federation allows identity systems from different organizations to trust each other, enabling users from one company to authenticate and communicate securely with users or resources hosted by another company without managing separate accounts.

Multifactor authentication enhances the security of an individual user's login within their own system but does not enable communication or identity recognition across different organizational domains.