Closed #1 (Add ability to disable sign up)

auth.php

@@ -19,9 +19,35 @@ function addUser($login, $password) {
 
 	$users = simplexml_load_file(PATH_TO_XML);
 
+	if (!$users->count()) {
+		$userWillBeAdmin = true;
+	}
 	$user = $users->addChild('user');
+	if (!empty($userWillBeAdmin)) {
+		$user->addAttribute('rights', 'admin');
+    }
 	$user->addChild('login', $login);
 	$user->addChild('password', $password);
 
 	$users->asXML(PATH_TO_XML);
 }
+
+function usersNumber() {
+	return simplexml_load_file(PATH_TO_XML)->count();
+}
+
+function hasAdminRights($login) {
+	$users = simplexml_load_file(PATH_TO_XML);
+
+	foreach ($users as $user) {
+		if ($user->login == $login) {
+			$rights = $user->attributes()['rights'];
+			$rights = explode(',', $rights);
+			foreach ($rights as $right) {
+				if (trim($right) == 'admin') return true;
+			}
+		}
+	}
+
+	return false;
+}

index.php

 <?php
 session_start();
+require 'auth.php';
 
 if (!isset($_SESSION['logged_in']) || !$_SESSION['logged_in']) : ?>
 
@@ -7,19 +8,21 @@ if (!isset($_SESSION['logged_in']) || !$_SESSION['logged_in']) : ?>
         <input type="text" name="login" placeholder="User name"><br>
         <input type="password" name="password" placeholder="Password"><br>
         <a href="signup.php">Sign up</a>
-        <button>Log in</button>
+        <button type="submit">Log in</button>
 
         <?php if (isset($_SESSION['login_failed']) && $_SESSION['login_failed']) : ?>
             <br><span style="color: red">Incorrect login or password</span>
         <?php $_SESSION['login_failed'] = false;
-        endif;
-        ?>
+        endif; ?>
     </form>
 
 <?php else : ?>
 
+    <?php if (hasAdminRights($_SESSION['login'])) : ?>
+        <a href="signup.php">Register user</a>
+    <?php endif; ?>
     <form action="logout.php">
-        <button>Log out</button>
+        <button type="submit">Log out</button>
     </form>
 
     Secret content

login.php

@@ -7,6 +7,7 @@ $password = $_POST['password'];
 
 if (authenticateUser($login, $password)) {
     $_SESSION['logged_in'] = true;
+    $_SESSION['login'] = $login;
 } else {
     $_SESSION['login_failed'] = true;
 }

logout.php

@@ -2,6 +2,7 @@
 session_start();
 
 $_SESSION['logged_in'] = false;
+$_SESSION['login'] = '';
 
 header("Location: index.php");
 die();
\ No newline at end of file

signup.php

 <?php
 require 'auth.php';
+session_start();
 
 switch ($_SERVER['REQUEST_METHOD']) {
     case 'GET': ?>