Linux PAM

• account modules check that the specified account is a valid authentication target under current conditions. This may include conditions like account expiration, time of day, and that the user has access to the requested service.
• authentication modules verify the user's identity, for example by requesting and checking a password or other secret. They may also pass authentication information on to other systems like a keyring.
• password modules are responsible for updating passwords, and are generally coupled to modules employed in the authentication step. They may also be used to enforce strong passwords.
• session modules define actions that are performed at the beginning and end of sessions. A session starts after the user has successfully authenticated.