include/pam_authenticate.hpp

#pragma once

#include <security/pam_appl.h>
#include <cstring>
#include <memory>
#include <boost/utility/string_view.hpp>

// function used to get user input
inline int pamFunctionConversation(int numMsg, const struct pam_message** msg,
                                   struct pam_response** resp,
                                   void* appdataPtr) {
  if (appdataPtr == nullptr) {
    return PAM_AUTH_ERR;
  }
  auto* pass = reinterpret_cast<char*>(
      malloc(std::strlen(reinterpret_cast<char*>(appdataPtr)) + 1));
  std::strcpy(pass, reinterpret_cast<char*>(appdataPtr));

  *resp = reinterpret_cast<pam_response*>(
      calloc(numMsg, sizeof(struct pam_response)));

  for (int i = 0; i < numMsg; ++i) {
    /* Ignore all PAM messages except prompting for hidden input */
    if (msg[i]->msg_style != PAM_PROMPT_ECHO_OFF) {
      continue;
    }

    /* Assume PAM is only prompting for the password as hidden input */
    resp[i]->resp = pass;
  }

  return PAM_SUCCESS;
}

inline bool pamAuthenticateUser(const boost::string_view username,
                                const boost::string_view password) {
  std::string userStr(username);
  std::string passStr(password);
  const struct pam_conv localConversation = {
      pamFunctionConversation, const_cast<char*>(passStr.c_str())};
  pam_handle_t* localAuthHandle = NULL;  // this gets set by pam_start

  if (pam_start("webserver", userStr.c_str(), &localConversation,
                &localAuthHandle) != PAM_SUCCESS) {
    return false;
  }
  int retval =
      pam_authenticate(localAuthHandle, PAM_SILENT | PAM_DISALLOW_NULL_AUTHTOK);

  if (retval != PAM_SUCCESS) {
    if (retval == PAM_AUTH_ERR) {
      // printf("Authentication failure.\n");
    } else {
      // printf("pam_authenticate returned %d\n", retval);
    }
    pam_end(localAuthHandle, PAM_SUCCESS);
    return false;
  }

  /* check that the account is healthy */
  if (pam_acct_mgmt(localAuthHandle, PAM_DISALLOW_NULL_AUTHTOK) !=
      PAM_SUCCESS) {
    pam_end(localAuthHandle, PAM_SUCCESS);
    return false;
  }

  if (pam_end(localAuthHandle, PAM_SUCCESS) != PAM_SUCCESS) {
    return false;
  }

  return true;
}