AD FS is an identity access solution that provides client computers (internal or external to your network) with seamless SSO access to protected Internet-facing applications or services, even when the user accounts and applications are located in completely different networks or organizations.
When an application or service is in one network and a user account is in another network, typically the user is prompted for secondary credentials when he or she attempts to access the application or service. These secondary credentials represent the user's identity in the realm where the or service resides. They are usually required by the Web server that hosts the application or service so that it can make the most appropriate authorization decision.
With AD FS, organizations can bypass requests for secondary credentials by providing trust relationships (federation trusts) that these organizations can use to project a user's digital identity and access rights to trusted partners. In this federated environment, each organization continues to manage its own identities, but each organization can also securely project and accept identities from other organizations.
Adding ClassLink as a relying trust partner will allow you to login to ClassLink with ADFS and access your ADFS applications with seamless single sign-on!