Last week I came across a scenario where Alternate Login ID feature of Active Directory Federation Services (AD FS) came at its best.
Part of an Enterprise Mobility Suite (EMS) implementation we were facing a challange to overcome. In this scenario the customer has multi-forest (fictive contoso.local & adatum.local) AD structure with a two-way forest trust relationship. The user resources are currently located in te frabrikam.local (blue) where all server resources are part of the contoso.local (grey) domain including AD FS.
As fabrikam.com is the public domain namespace used, we added a UPN suffix for the fabrikam.local domain to make sure the user objects synced from the on-premise Active Directory – by Azure Active Directory Sync – matches the public User Principal Name (UPN) domain namespace.