Implement basic login function; add basic styling

src/Frontend/Login/LoginController.php

@@ -0,0 +1,63 @@
+<?php
+declare(strict_types=1);
+
+namespace MailAccountAdmin\Frontend\Login;
+
+use Psr\Http\Message\ResponseInterface as Response;
+use Psr\Http\Message\ServerRequestInterface as Request;
+use Slim\Exception\HttpBadRequestException;
+use Slim\Views\Twig;
+
+class LoginController
+{
+    /** @var Twig */
+    private $view;
+
+    public function __construct(Twig $view)
+    {
+        $this->view = $view;
+    }
+
+    public function showLoginPage(Request $request, Response $response): Response
+    {
+        if (!empty($_SESSION['username'])) {
+            // Already logged in, redirect to dashboard
+            return $response
+                ->withHeader('Location', '/')
+                ->withStatus(303);
+        }
+
+        $renderData = [
+        ];
+
+        return $this->view->render($response, 'login.html.twig', $renderData);
+    }
+
+    public function authenticateUser(Request $request, Response $response): Response
+    {
+        $params = (array)$request->getParsedBody();
+
+        if (empty($params['username']) || empty($params['password'])) {
+            throw new HttpBadRequestException($request, 'Missing parameters');
+        }
+
+        // TODO: only for testing, obviously
+        if ($params['username'] === 'lexi' && $params['password'] === 'testpw') {
+            $_SESSION['username'] = $params['username'];
+            return $response
+                ->withHeader('Location', '/')
+                ->withStatus(303);
+        } else {
+            return $this->view->render($response, 'login.html.twig', ['error' => 'Wrong username or password!']);
+        }
+    }
+
+    public function logoutUser(Request $request, Response $response): Response
+    {
+        session_destroy();
+
+        return $response
+            ->withHeader('Location', '/login')
+            ->withStatus(303);
+    }
+}