CADC User Authorization Model
The CADC User Authorization Model is a model for representing CADC users and groups. The model is used primarily in the GMS and Users Web services.

User Class Features
In the system, a user is uniquely identified by one Principal (in CADC's case that is of type NumericPrincipal) but can have a number of other identities for different contexts:- HttpPrincipal: Web user identity associated with Simple HHTP User Password access.
- X500Principal: X509 certificate identity.
- NumericPrincipal: An numeric identity associated with a user. Typically, used internally within a system.
- OpenIdPrincipal: An OpenID identity.