functions.php

<?php

// Copyright 2014 yAzZiE Labs
//
// This file is part of php-admin-login.
//
// php-admin-login is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// any later version.
//
// php-admin-login is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with php-admin-login. If not, see <http://www.gnu.org/licenses/>.

$loginPassword = 'Facepunch'; // This is the plain-text password, change this to whatever you want to use as a password.
$md5LoginPassword = md5($loginPassword); // If you want to store your password in MD5 form only, delete the above line and replace "md5($loginPassword)" with your MD5 hash.
$phpSessionName = 'php-admin-login'; // Name of the PHP Session used to store the MD5 hashed password. You can change this to avoid interference with other websites that may use this same login code.

$loginPasswordPOST = $_POST["password"];
session_start(); $md5LoginPasswordSession = $_SESSION[$phpSessionName];

function logIn() {
global $loginPassword;
global $md5LoginPassword;
global $loginPasswordPOST;
global $md5LoginPasswordSession;
global $phpSessionName;
$md5LoginPasswordPOST = md5($loginPasswordPOST);
if ($md5LoginPasswordPOST === $md5LoginPassword) {session_start(); $_SESSION[$phpSessionName]=$md5LoginPasswordPOST; loginSuccess(); };
if ($md5LoginPasswordSession !== $md5LoginPassword) {loginFailed("invalid"); };
if ($md5LoginPasswordSession === $md5LoginPassword) {loginSuccess(); };
};

function loginErrorMessage() {
	$loginErrorReason = $_GET['failed'];
	if ($loginErrorReason === 'denied') {echo 'Access is denied or your session has expired. Please enter your password.'; }; // Login Error Explanation if a user tries to access a password protected page when they aren't logged in.
	if ($loginErrorReason === 'invalid') {echo 'The password you entered is incorrect. Please try again.'; }; // Login Error Explanation if the user didn't enter the correct password.
};

function loginFailed($reason) {
	header("HTTP/1.1 301 Moved Permanently"); 
	header("Location: login.php?failed={$reason}"); // User is redirected back to the login page with a corresponding error message (generated by loginErrorMessage() above) as to why their login failed.
	exit;
};
	
function loginSuccess() {
	header("HTTP/1.1 301 Moved Permanently"); 
	header("Location: demo.php"); // Where the user is redirected to when they log in.
	exit;
};
	
function logOut() {
	global $phpSessionName;
	session_start();
	unset($_SESSION[$phpSessionName]);
	session_destroy();
	header("HTTP/1.1 301 Moved Permanently"); 
	header("Location: login.php"); // Where the user is redirected to when they log out.
	exit;
};
	
?>