diff --git a/AddOn/Calender_Office365/GraphCalendar.php b/AddOn/Calender_Office365/GraphCalendar.php
new file mode 100644
index 00000000..c452ab89
--- /dev/null
+++ b/AddOn/Calender_Office365/GraphCalendar.php
@@ -0,0 +1,305 @@
+<?php
+
+/**
+ * Klasse zur Interaktion mit dem Microsoft Graph API für Kalenderfunktionen.
+ */
+class GraphCalendar
+{
+    // Konfigurationswerte und interne Felder
+    private $clientId;
+    private $clientSecret;
+    private $tenantId;
+    private $graphUrl = 'https://graph.microsoft.com/v1.0'; // Basis-URL für das Microsoft Graph API
+    private $token;
+    private $headers;
+    private $defaultUserEmail;
+
+    /**
+     * Konstruktor: Initialisiert mit Azure AD App-Credentials und optionaler Standard-E-Mail.
+     */
+    public function __construct($clientId, $clientSecret, $tenantId, $defaultUserEmail = null)
+    {
+        $this->clientId     = $clientId;
+        $this->clientSecret = $clientSecret;
+        $this->tenantId     = $tenantId;
+        $this->defaultUserEmail = $defaultUserEmail;
+
+        // Authentifizierung gegen Microsoft Graph API durchführen
+        $this->authenticate();
+    }
+
+    /**
+     * Authentifiziert sich mit dem Client-Credentials-Flow (ohne Benutzerinteraktion)
+     */
+    private function authenticate()
+    {
+        $tokenUrl = "https://login.microsoftonline.com/{$this->tenantId}/oauth2/v2.0/token";
+
+        // Daten für den OAuth2 Token-Request
+        $data = [
+            'grant_type' => 'client_credentials',
+            'client_id' => $this->clientId,
+            'client_secret' => $this->clientSecret,
+            'scope' => 'https://graph.microsoft.com/.default', // Zugriff auf alle berechtigten Graph APIs
+        ];
+
+        // Token abrufen
+        $response = $this->postCurl($tokenUrl, ['Content-Type: application/x-www-form-urlencoded'], $data);
+        $decoded = json_decode($response, true);
+        $this->token = $decoded['access_token'];
+
+        // Standard-Header für alle API-Requests
+        $this->headers = [
+            "Authorization: Bearer {$this->token}",
+            "Content-Type: application/json"
+        ];
+    }
+
+    /**
+     * Gibt eine gültige Benutzer-E-Mail zurück oder wirft einen Fehler
+     */
+    private function resolveUserEmail($userEmail)
+    {
+        if (!empty($userEmail)) {
+            return $userEmail;
+        } elseif (!empty($this->defaultUserEmail)) {
+            return $this->defaultUserEmail;
+        } else {
+            throw new Exception("Keine Benutzer-E-Mail angegeben.");
+        }
+    }
+
+    /**
+     * Gibt alle oder ein bestimmtes Kalender-Event zurück
+     */
+    public function getEvents($eventId = "", $userEmail = "")
+    {
+        $email = $this->resolveUserEmail($userEmail);
+
+        if($eventId == ""){
+            // Alle Events des Nutzers abrufen
+            $eventsResponse = $this->getCurl("$this->graphUrl/users/{$email}/calendar/events", $this->headers);
+            return json_decode($eventsResponse, true)['value'] ?? [];
+        } else {
+            // Nur ein einzelnes Event anhand der ID abrufen
+            $eventsResponse = $this->getCurl("{$this->graphUrl}/users/{$email}/calendar/events/{$eventId}", $this->headers);
+            return json_decode($eventsResponse, true) ?? [];
+        }
+    }
+
+    /**
+     * Erstellt ein neues Kalender-Event (mit optionalem Teams-Link und Teilnehmern)
+     */
+    public function createEvent($subject, $startTime, $endTime, $isTeamsTermin = false, $description = '', $location = "", $gustArray = array(), $userEmail = "", $timezone = 'Europe/Berlin')
+    {
+        $email = $this->resolveUserEmail($userEmail);
+
+        // Event-Daten vorbereiten
+        $event = [
+            'subject' => $subject,
+            'start' => [
+                'dateTime' => $startTime,
+                'timeZone' => $timezone
+            ],
+            'end' => [
+                'dateTime' => $endTime,
+                'timeZone' => $timezone
+            ],
+            'body' => [
+                'contentType' => 'HTML',
+                'content' => $description
+            ],
+            'location' => [
+                'displayName' => $location
+            ]
+        ];
+
+        // Optional: Teams-Termin aktivieren
+        if($isTeamsTermin == true){
+            $event['isOnlineMeeting'] = true;
+            $event['onlineMeetingProvider'] = 'teamsForBusiness';
+        }
+
+        // Teilnehmer hinzufügen, falls vorhanden
+        if(count($gustArray) > 0){
+            $event['attendees'] = $gustArray;
+        }
+
+        // Event erstellen
+        $url = "{$this->graphUrl}/users/{$email}/calendar/events";
+        $response = $this->postJsonCurl($url, $this->headers, $event);
+        return json_decode($response, true);
+    }
+
+    /**
+     * Bestehendes Event aktualisieren
+     */
+    public function updateEvent($eventId, $subject, $startTime, $endTime, $isTeamsTermin = false, $description = '', $location = "", $gustArray = array(), $userEmail = "", $timezone = 'Europe/Berlin')
+    {
+        $email = $this->resolveUserEmail($userEmail);
+
+        // Neue Eventdaten
+        $event = [
+            'subject' => $subject,
+            'start' => [
+                'dateTime' => $startTime,
+                'timeZone' => $timezone
+            ],
+            'end' => [
+                'dateTime' => $endTime,
+                'timeZone' => $timezone
+            ],
+            'body' => [
+                'contentType' => 'HTML',
+                'content' => $description
+            ],
+            'location' => [
+                'displayName' => $location
+            ],
+            'isOnlineMeeting' => $isTeamsTermin
+        ];
+
+        // Teams-Link ggf. setzen
+        if($isTeamsTermin == true){
+            $event['onlineMeetingProvider'] = 'teamsForBusiness';
+        }
+
+        // Teilnehmer aktualisieren
+        if(count($gustArray) > 0){
+            $event['attendees'] = $gustArray;
+        }
+
+        // Event patchen (aktualisieren)
+        $url = "{$this->graphUrl}/users/{$email}/calendar/events/{$eventId}";
+        $result = $this->patchJsonCurl($url, $this->headers, $event);
+        return [
+            'status' => $result['status'],
+            'response' => json_decode($result['response'], true)
+        ];
+    }
+
+    /**
+     * Löscht ein Kalender-Event anhand der ID
+     */
+    public function deleteEvent($eventId, $userEmail = "")
+    {
+        $email = $this->resolveUserEmail($userEmail);
+        $url = "{$this->graphUrl}/users/{$email}/calendar/events/{$eventId}";
+        return $this->deleteCurl($url, $this->headers);
+    }
+
+    /**
+    * Hängt eine Datei als Attachment an ein Kalender-Event.
+    *
+    * @param string $eventId Die ID des Events
+    * @param string $fileName Der Dateiname (z.B. "dokument.pdf")
+    * @param string $fileContent Der Inhalt der Datei als Base64-kodierter String
+    * @param string $contentType Der MIME-Typ der Datei (z.B. "application/pdf")
+    * @param string $userEmail Optional: Benutzer-E-Mail, falls abweichend
+    * @return array Antwort von der Graph API
+    */
+    public function addAttachmentToEvent($eventId, $fileName, $fileContent, $contentType = 'application/octet-stream', $userEmail = '')
+    {
+        $email = $this->resolveUserEmail($userEmail);
+
+        // Attachment-Objekt
+        $attachment = [
+            '@odata.type' => '#microsoft.graph.fileAttachment',
+            'name' => $fileName,
+            'contentType' => $contentType,
+            'contentBytes' => base64_encode($fileContent)
+        ];
+
+        $url = "{$this->graphUrl}/users/{$email}/events/{$eventId}/attachments";
+        $response = $this->postJsonCurl($url, $this->headers, $attachment);
+
+        return json_decode($response, true);
+    }
+
+
+    // === HELPER-FUNKTIONEN FÜR CURL ===
+
+    /**
+     * POST-Request mit URL-encoded Daten
+     */
+    private function postCurl($url, $headers, $data)
+    {
+        $ch = curl_init($url);
+        curl_setopt_array($ch, [
+            CURLOPT_RETURNTRANSFER => true,
+            CURLOPT_POST => true,
+            CURLOPT_HTTPHEADER => $headers,
+            CURLOPT_POSTFIELDS => http_build_query($data),
+        ]);
+        $response = curl_exec($ch);
+        curl_close($ch);
+        return $response;
+    }
+
+    /**
+     * GET-Request
+     */
+    private function getCurl($url, $headers)
+    {
+        $ch = curl_init($url);
+        curl_setopt_array($ch, [
+            CURLOPT_RETURNTRANSFER => true,
+            CURLOPT_HTTPHEADER => $headers,
+        ]);
+        $response = curl_exec($ch);
+        curl_close($ch);
+        return $response;
+    }
+
+    /**
+     * POST-Request mit JSON-Daten
+     */
+    private function postJsonCurl($url, $headers, $json)
+    {
+        $ch = curl_init($url);
+        curl_setopt_array($ch, [
+            CURLOPT_RETURNTRANSFER => true,
+            CURLOPT_POST => true,
+            CURLOPT_HTTPHEADER => $headers,
+            CURLOPT_POSTFIELDS => json_encode($json),
+        ]);
+        $response = curl_exec($ch);
+        curl_close($ch);
+        return $response;
+    }
+
+    /**
+     * PATCH-Request (teilweises Update von Ressourcen)
+     */
+    private function patchJsonCurl($url, $headers, $json)
+    {
+        $ch = curl_init($url);
+        curl_setopt_array($ch, [
+            CURLOPT_RETURNTRANSFER => true,
+            CURLOPT_CUSTOMREQUEST => 'PATCH',
+            CURLOPT_HTTPHEADER => $headers,
+            CURLOPT_POSTFIELDS => json_encode($json),
+        ]);
+        $response = curl_exec($ch);
+        $httpCode = curl_getinfo($ch, CURLINFO_HTTP_CODE);
+        curl_close($ch);
+        return ['status' => $httpCode, 'response' => $response];
+    }
+
+    /**
+     * DELETE-Request
+     */
+    private function deleteCurl($url, $headers)
+    {
+        $ch = curl_init($url);
+        curl_setopt_array($ch, [
+            CURLOPT_RETURNTRANSFER => true,
+            CURLOPT_CUSTOMREQUEST => 'DELETE',
+            CURLOPT_HTTPHEADER => $headers,
+        ]);
+        $response = curl_exec($ch);
+        $httpCode = curl_getinfo($ch, CURLINFO_HTTP_CODE);
+        curl_close($ch);
+        return $httpCode;
+    }
+}