Refactor authentication system (#2602)

Make auth configuration available via UI, remove FOSUserBundle and SAML-Bundle dependency

src/Validator/Constraints/User.php

@@ -0,0 +1,35 @@
+<?php
+
+/*
+ * This file is part of the Kimai time-tracking app.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace App\Validator\Constraints;
+
+use Doctrine\Common\Annotations\Annotation\Target;
+use Symfony\Component\Validator\Constraint;
+
+/**
+ * @Annotation
+ * @Target({"CLASS", "PROPERTY", "METHOD", "ANNOTATION"})
+ */
+class User extends Constraint
+{
+    public const USER_EXISTING_EMAIL = 'kimai-user-00';
+    public const USER_EXISTING_NAME = 'kimai-user-01';
+
+    protected static $errorNames = [
+        self::USER_EXISTING_EMAIL => 'The email is already used.',
+        self::USER_EXISTING_NAME => 'The username is already used.',
+    ];
+
+    public $message = 'The user has invalid settings.';
+
+    public function getTargets()
+    {
+        return self::CLASS_CONSTRAINT;
+    }
+}