I would like to authenticate users of my C network application with PAM and I have a found a nice PAM example here on Stack, which I attach at the bottom. The problem is that in my development machine I have a fingerprint reader which PAM is set up to use, as in /etc/pam.d/common-auth:
#%PAM-1.0
#
# This file is autogenerated by pam-config. All changes
# will be overwritten.
#
# Authentication-related modules common to all services
#
# This file is included from other service-specific PAM config files,
# and should contain a list of the authentication modules that define
# the central authentication scheme for use on the system
# (e.g., /etc/shadow, LDAP, Kerberos, etc.). The default is to use the
# traditional Unix authentication mechanisms.
#
auth required pam_env.so
auth sufficient pam_fprint.so
auth optional pam_gnome_keyring.so
auth required pam_unix2.so
pam_fprint.so is the fingerprint reader plugin. When you normally log in, the scan can fail and you are prompted for a password. However, sshd daemon does not initiate the fingerprint at all and I would like to understand how it skips it, because for example /etc/pam.d/sshd references the common-auth module so it must pull it ..
#%PAM-1.0
auth requisite pam_nologin.so
auth include common-auth
account requisite pam_nologin.so
account include common-account
password include common-password
session required pam_loginuid.so
session include common-session
session optional pam_lastlog.so silent noupdate showfailed
I have tried to reference the 'sshd' scheme from the C program but it still initiates the fingerprint reader. I want to skip the fingerprint reader somehow in C and retain my fingerprint reader default config.
#include <stdlib.h>
#include <iostream>
#include <fstream>
#include <security/pam_appl.h>
#include <unistd.h>
// To build this:
// g++ test.cpp -lpam -o test
struct pam_response *reply;
//function used to get user input
int function_conversation(int num_msg, const struct pam_message **msg, struct pam_response **resp, void *appdata_ptr)
{
*resp = reply;
return PAM_SUCCESS;
}
int main(int argc, char** argv)
{
if(argc != 2) {
fprintf(stderr, "Usage: check_user <username>\n");
exit(1);
}
const char *username;
username = argv[1];
const struct pam_conv local_conversation = { function_conversation, NULL };
pam_handle_t *local_auth_handle = NULL; // this gets set by pam_start
int retval;
// local_auth_handle gets set based on the service
retval = pam_start("common-auth", username, &local_conversation, &local_auth_handle);
if (retval != PAM_SUCCESS)
{
std::cout << "pam_start returned " << retval << std::endl;
exit(retval);
}
reply = (struct pam_response *)malloc(sizeof(struct pam_response));
// *** Get the password by any method, or maybe it was passed into this function.
reply[0].resp = getpass("Password: ");
reply[0].resp_retcode = 0;
retval = pam_authenticate(local_auth_handle, 0);
if (retval != PAM_SUCCESS)
{
if (retval == PAM_AUTH_ERR)
{
std::cout << "Authentication failure." << std::endl;
}
else
{
std::cout << "pam_authenticate returned " << retval << std::endl;
}
exit(retval);
}
std::cout << "Authenticated." << std::endl;
retval = pam_end(local_auth_handle, retval);
if (retval != PAM_SUCCESS)
{
std::cout << "pam_end returned " << retval << std::endl;
exit(retval);
}
return retval;
}