/*
 * user-test.c - ask a user for their password, and compare it to
 *                       the password, as taken from the "/etc/passwd" file.
 */

#include <unistd.h>   /* crypt(), etc.          */
#include <pwd.h>      /* getpass(), getpwnam(). */
#include <string.h>   /* strcmp(), etc.         */
#include <stdlib.h>
#include <stdio.h>
#define _XOPEN_SOURCE

int
main()
{
    /* buffers for reading in the user name and the password. */
    char user[21];
    char* password;
    /* storing the encrypted password, and the salt. */
    char* encrypted_password;
    char salt[2];
    /* user's "/etc/passwd" entry. */
    struct passwd* user_info;

    /* prompt the user for a user name. */
    printf("User name: ");
    fflush(stdout); /* flush the prompt to make sure the user sees it. */
    fgets(user, 20, stdin);
    /* fgets() stores also the new-line that the user typed in. so we */
    /* need to locate the new-line character, and truncate it.        */
    if (strchr(user, '\n'))
	(*(strchr(user, '\n'))) = '\0';

    /* prompt the user for their password. the getpass() function  */
    /* prints the given prompt, turns off echo (so the password    */
    /* typed won't be seen on screen), and returns the string that */
    /* the user types.                                             */
    password = getpass("Password: ");

    /* find the user's encrypted password, as stored in "/etc/passwd". */
    user_info = getpwnam(user);
    if (!user_info) {
        printf("login incorrect.\n");
        return 1;
    }

    /* take the salt as stored in the password field of the user. */
    strncpy(salt, user_info->pw_passwd, 2);

    /* encrypt the given password using the found "salt". */
    encrypted_password = crypt(password, salt);

    /* compare the results of crypt, with the user's stored password field. */
    if (strcmp(user_info->pw_passwd, encrypted_password) != 0) {
        printf("login incorrect.\n");
        return 1;
    }

    /* authentication succeeded... */
    printf("login successful.\n");
    return 0;
}