Claims-based identity

Claims-based identity is a common way for applications to acquire the identity information they need about users inside their organization, in other organizations, and on the Internet. It also provides a consistent approach for applications running on-premises or in the cloud. Claims-based identity abstracts the individual elements of identity and access control into two parts: a notion of claims, and the concept of an issuer or an authority.

A claim is a statement that one subject, such as a person or organization, makes about itself or another subject. For example, the statement can be about a name, group, buying preference, ethnicity, privilege, association or capability. The subject making the claim or claims is the provider. Claims are packaged into one or more tokens that are then issued by an issuer (provider), commonly known as a security token service (STS).

The name "claims-based identity" can be confusing at first because it seems like a misnomer. Attaching the concept of claims to the concept of identity appears to be combining authentication (determination of identity) with authorization (what the identified subject may and may not do). However a closer examination reveals that this is not the case. Claims are not what the subject can and cannot do. They are what the subject is or is not. It is up to the application receiving the incoming claim to map the is/is not claims to the may/may not rules of the application. In traditional systems there is often confusion about the differences and similarities between what a user is/is not and what the user may/may not do. Claims-based identity makes that distinction clear.

Once the distinction between what the user is/is not and what the user may/may not do is clarified, it becomes apparent that the authentication of what the user is/is not (the claims) are often better handled by a third party than by any individual application. This third party is called the security token service. To better understand the concept of security token service, consider the analogy of a night club with a doorman. The doorman wants to prevent under-age patrons from entry. To facilitate this he requests a patron to present a driver's license, health insurance card or other identification (the token) that has been issued by a trusted third party (the security token service) such as the provincial or state vehicle license department, health department or insurance company. The nightclub is thus alleviated of the responsibility of determining the patron's age. It only has to trust the issuing authority (and of course make its own judgment of the authenticity of the token presented). With these two steps completed the nightclub has successfully authenticated the patron with regard to the claim that he or she is of legal drinking age.

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