pamauthenticate

pamauthenticate, commonly referring to the PAM API function pam_authenticate, is a routine used by applications to perform user authentication within the Pluggable Authentication Modules (PAM) framework. It delegates credential verification to the authentication stack configured for a given service, such as login, sudo, or ssh, by querying the configured PAM modules.

To use pam_authenticate, an application typically initializes a PAM handle with pam_start, sets the PAM_USER item to the username, and provides a conversation function (pam_conv) that handles prompts from modules. The actual authentication is performed by the modules in the stack for the selected service, which may prompt for a password or other credentials via the conversation interface. The function does not create a login session by itself; it verifies credentials and may be followed by subsequent PAM calls (for example, to open a session) as part of a complete authentication flow.

The return value of pam_authenticate indicates the outcome of the authentication attempt. A return of PAM_SUCCESS means the user was authenticated. Other common codes include PAM_AUTH_ERR for a failed authentication, PAM_USER_UNKNOWN if the user does not exist, PAM_NEW_AUTHTOK_REQD when a password change is required, and PAM_CRED_INSUFFICIENT or PAM_SERVICE_ERR for various failure conditions. Additional codes such as PAM_BUF_ERR, PAM_CONV_ERR, and PAM_SYSTEM_ERR may indicate underlying resource or configuration issues. The exact codes depend on the modules and the PAM configuration in /etc/pam.d.

In summary, pam_authenticate is a core function of PAM that enables applications to verify user credentials through a modular stack, abstracting the specifics of authentication mechanisms behind the PAM configuration. It is typically used as part of a broader authentication workflow that may include session management and credential updates.