pam_sm_authenticate(3)

NAME

pam_sm_authenticate — Service provider implementation for pam_authenticate

SYNOPSIS

cc [ flag ... ] file ... -lpam [ library ... ]

#include <security/pam_appl.h>

#include <security/pam_modules.h>

int pam_sm_authenticate(pam_handle_t *pamh, int flags, int argc, const char **argv);

DESCRIPTION

In response to a call to pam_authenticate(3), the PAM framework calls pam_sm_authenticate() from the modules listed in the pam.conf(4) file. The authentication provider supplies the back-end functionality for this interface function.

The function, pam_sm_authenticate(), is called to verify the identity of the current user. The user is usually required to enter a password or similar authentication token depending upon the authentication scheme configured within the system. The user in question is specified by a prior call to pam_start(), and is referenced by the authentication handle, pamh.

If the user is unknown to the authentication service, the service module should mask this error and continue to prompt the user for a password. It should then return the error, PAM_USER_UNKNOWN.

The following flag may be passed in to pam_sm_authenticate():

PAM_SILENT: The authentication service should not generate any messages.
PAM_DISALLOW_NULL_AUTHTOK: The authentication service should return PAM_AUTH_ERROR if the user has a null authentication token.

The argc argument represents the number of module options passed in from the configuration file pam.conf(4). argv specifies the module options, which are interpreted and processed by the authentication service. Please refer to the specific module manual pages for the various available options. If any unknown option is passed in, the module should log the error and ignore the option.

Before returning, pam_sm_authenticate() should call pam_get_item() and retrieve PAM_AUTHTOK. If it has not been set before (ie. the value is NULL), pam_sm_authenticate() should set it to the password entered by the user using pam_set_item().

An authentication module may save the authentication status (success or reason for failure) as state in the authentication handle using pam_set_data(). This information is intended for use by pam_setcred().

APPLICATION USAGE

Refer to pam(3) for information on thread-safety of PAM interfaces.

NOTES

Modules should not retry the authentication in the event of a failure. Applications handle authentication retries and maintain the retry count. To limit the number of retries, the module can return a PAM_MAXTRIES error.

RETURN VALUES

Upon successful completion, PAM_SUCCESS must be returned. In addition, the following values may be returned:

PAM_MAXTRIES: Maximum number of authentication attempts exceeded.
PAM_AUTH_ERR: Authentication failure.
PAM_CRED_INSUFFICIENT: Can not access authentication data due to insufficient credentials.
PAM_AUTHINFO_UNAVAIL: Underlying authentication service can not retrieve authentication information.
PAM_USER_UNKNOWN: User not known to underlying authentication module.
PAM_IGNORE: Ignore underlying authentication module regardless of whether the control flag is required, optional or sufficient.

pam_sm_authenticate(3)

Technical documentation

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