The System.IdentityModel.Claims namespace provides types that support the use of claims in the Extensible Identity Model.
Identity Model is a claims-based system. Claims describe the capabilities associated with some entity in the system, often a user of that system. The set of claims associated with a given entity can be thought of as a key. The particular claims define the shape of that key; much like a physical key is used to open a lock in a door. In this way, claims are used to gain access to resources. Access to a given protected resource is determined by comparing the claims required to access that resource with the claims associated with the entity attempting access.
A claim is the expression of a right with respect to a particular value. A right could be something like "Read" or "Write". A value could be a database, a file, a mailbox, or a property. Claims also have a claim type. The combination of claim type and right provides the mechanism for capabilities being specified with respect to the value. For example, a claim of type "File" with right "Read" over the value "Biography.doc" indicates that the entity with which such a claim is associated has read access to the file Biography.doc. A claim of type "Name" with right "PossessProperty" over the value "Martin" indicates that the entity with which such a claim is associated possesses a Name property with the value "Martin."
Although various claim types and rights are defined as part of Identity Model, the system is extensible. The various systems building on top of the Identity Model infrastructure can define claim types and rights as required.