feat: smtp sending

Signed-off-by: Sebastian Krupinski <krupinski01@gmail.com>

lib/Smtp/Auth/AuthMechanism.php

@@ -0,0 +1,44 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: Sebastian Krupinski <krupinski01@gmail.com>
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace KTXM\ProviderImap\Smtp\Auth;
+
+/**
+ * Supported SASL authentication mechanisms, in preference order.
+ */
+enum AuthMechanism: string
+{
+    case Plain = 'PLAIN';
+    case Login = 'LOGIN';
+
+    /**
+     * Select the most preferred mechanism the server advertises.
+     *
+     * @param list<string> $advertised mechanisms offered by the server (uppercased)
+     */
+    public static function select(array $advertised): ?self
+    {
+        foreach ([self::Plain, self::Login] as $mechanism) {
+            if (in_array($mechanism->value, $advertised, true)) {
+                return $mechanism;
+            }
+        }
+
+        return null;
+    }
+
+    /**
+     * The initial AUTH response for the PLAIN mechanism:
+     * base64( authzid NUL authcid NUL passwd ).
+     */
+    public static function plainToken(string $username, string $password): string
+    {
+        return base64_encode("\0" . $username . "\0" . $password);
+    }
+}