Federation is a process that allows for the conveyance of authentication and subscriber attribute information across networked systems. In a federation scenario, the verifier or CSP is referred to as an identity provider, or IdP. The RP is the party that receives and uses the information provided by the IdP.

Federated identity systems use assertions to accomplish this task. Assertions are statements from an IdP to an RP that contain information about a subscriber. Federation technology is generally used when the RP and the IdP are not a single entity or are not under common administration. The RP uses the information in the assertion to identify the subscriber and make authorization decisions about their access to resources controlled by the RP. An assertion typically includes an identifier for the subscriber, allowing association of the subscriber with their previous interactions with the RP. Assertions may additionally include attribute values or attribute references that further characterize the subscriber and support the authorization decision at the RP. Additional attributes may also be available outside of the assertion as part of the larger federation protocol. These attribute values and attribute references are often used in determining access privileges for Attribute Based Access Control (ABAC) or facilitating a transaction (e.g., shipping address).

In a federated identity scenario, the subscriber does not authenticate directly to the RP. Instead, the federation protocol defines a mechanism for an IdP to generate an assertion for the identifier associated with a subscriber, usually in response to a request from the RP. The IdP is responsible for authenticating the subscriber (though it may use session management as described in SP 800- 63B, Section 7). This process allows the subscriber to obtain services from multiple RPs without the need to hold or maintain separate credentials at each. This process can also be used to support single sign on, where subscribers authenticate once to an IdP and subsequently obtain services from multiple RPs. …

Quelle / Link: Digital Identity Guidelines Federation and Assertions