Authentication is the process of determining whether someone or something is, in fact, who or what it declares itself to be. Authentication technology provides access control for systems by checking to see if a user's credentials match the credentials in a database of authorized users or in a data authentication server.
Users are usually identified with a user ID, and authentication is accomplished when the user provides a credential, for example, a Password, that matches that user ID. Most users are most familiar with using a password, which, as a piece of information that should be known only to the user, is called a knowledge authentication factor. Other authentication factors, and how they are used for two-factor or multifactor authentication (MFA)