What is ADFS?

Active Directory Federation Services (ADFS) is a feature and web service in the Windows Server Operating System that allows sharing of identity information outside a company’s network. It authenticates users with their usernames and passwords. Users can access some applications (for example Office 365, Salesforce.com, other custom web apps, etc.) without being prompted to provide login credentials again. These applications can be on premise, on the cloud, or even hosted by third parties