Software Architect's Handbook

Authentication

Authentication is the process of determining if someone (or something) is who (or what) they claim to be. It deals primarily with validating the identity of a subject. Examples of a subject that may need to be authenticated include a user, a service, a computer, or an application.

In the early days of software development, applications would commonly maintain their own user profiles for authentication, which would include some type of unique identifier (for example, a username or email address) and a password. Users provide their identifier and password and, if they match with the values the application has for a user profile, then the user is considered to be authenticated.