include/pam_authenticate.hpp

#pragma once

#include <security/pam_appl.h>

#include <boost/utility/string_view.hpp>

#include <cstring>
#include <memory>

// 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;
    }
    char* appPass = reinterpret_cast<char*>(appdataPtr);
    size_t appPassSize = std::strlen(appPass);
    char* pass = reinterpret_cast<char*>(malloc(appPassSize + 1));
    if (pass == nullptr)
    {
        return PAM_AUTH_ERR;
    }

    std::strncpy(pass, appPass, appPassSize + 1);

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

    if (resp == nullptr)
    {
        free(pass);
        return PAM_AUTH_ERR;
    }

    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;
}

/**
 * @brief Attempt username/password authentication via PAM.
 * @param username The provided username aka account name.
 * @param password The provided password.
 * @returns PAM error code or PAM_SUCCESS for success. */
inline int pamAuthenticateUser(const std::string_view username,
                               const std::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 = nullptr; // this gets set by pam_start

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

    retval = pam_authenticate(localAuthHandle,
                              PAM_SILENT | PAM_DISALLOW_NULL_AUTHTOK);
    if (retval != PAM_SUCCESS)
    {
        pam_end(localAuthHandle, PAM_SUCCESS); // ignore retval
        return retval;
    }

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

    return pam_end(localAuthHandle, PAM_SUCCESS);
}

inline int pamUpdatePassword(const std::string& username,
                             const std::string& password)
{
    const struct pam_conv localConversation = {
        pamFunctionConversation, const_cast<char*>(password.c_str())};
    pam_handle_t* localAuthHandle = nullptr; // this gets set by pam_start

    int retval = pam_start("webserver", username.c_str(), &localConversation,
                           &localAuthHandle);

    if (retval != PAM_SUCCESS)
    {
        return retval;
    }

    retval = pam_chauthtok(localAuthHandle, PAM_SILENT);
    if (retval != PAM_SUCCESS)
    {
        pam_end(localAuthHandle, PAM_SUCCESS);
        return retval;
    }

    return pam_end(localAuthHandle, PAM_SUCCESS);
}