An authentication mechanism is a process or method used to verify the identity of a user or system attempting to access a resource or service. It involves the use of credentials such as usernames, passwords, biometric data, or digital certificates to confirm the identity of the user or system. Authentication mechanisms are used to ensure that only authorized users or systems are granted access to sensitive information or resources. Examples of authentication mechanisms include single sign-on (SSO), multi-factor authentication (MFA), and Kerberos authentication.