refactor: reuse the SSO app registration for M365 calendar sync

One Entra enterprise application now covers both interactive login and
the calendar sync's client-credentials Graph access, instead of
requiring a second app registration. GraphClientService reads
OIDC_ISSUER_URL/OIDC_CLIENT_ID/OIDC_CLIENT_SECRET (same as SSO) and
derives the tenant ID from the issuer URL's path, rather than three
dedicated M365_CALENDAR_* env vars. The app registration just needs the
"Calendars.ReadWrite" Application permission added alongside its
existing delegated login scopes.

Co-Authored-By: Claude Sonnet 5 <[email protected]>

ApiCore-Backend/src/calendar-sync/graph-client.service.spec.ts

@@ -17,30 +17,36 @@ describe('GraphClientService', () => {
     service = new GraphClientService();
     fetchMock = jest.fn();
     global.fetch = fetchMock;
-    process.env.M365_CALENDAR_TENANT_ID = 'tenant-1';
-    process.env.M365_CALENDAR_CLIENT_ID = 'client-1';
-    process.env.M365_CALENDAR_CLIENT_SECRET = 'secret-1';
+    process.env.OIDC_ISSUER_URL =
+      'https://login.microsoftonline.com/tenant-1/v2.0';
+    process.env.OIDC_CLIENT_ID = 'client-1';
+    process.env.OIDC_CLIENT_SECRET = 'secret-1';
   });
 
   afterEach(() => {
-    delete process.env.M365_CALENDAR_TENANT_ID;
-    delete process.env.M365_CALENDAR_CLIENT_ID;
-    delete process.env.M365_CALENDAR_CLIENT_SECRET;
+    delete process.env.OIDC_ISSUER_URL;
+    delete process.env.OIDC_CLIENT_ID;
+    delete process.env.OIDC_CLIENT_SECRET;
   });
 
   describe('isConfigured', () => {
-    it('returns true when all three env vars are set', () => {
+    it('returns true when all three SSO env vars are set', () => {
       expect(service.isConfigured()).toBe(true);
     });
 
     it('returns false when a required env var is missing', () => {
-      delete process.env.M365_CALENDAR_CLIENT_SECRET;
+      delete process.env.OIDC_CLIENT_SECRET;
+      expect(service.isConfigured()).toBe(false);
+    });
+
+    it('returns false when the issuer URL has no tenant segment', () => {
+      process.env.OIDC_ISSUER_URL = 'https://login.microsoftonline.com/';
       expect(service.isConfigured()).toBe(false);
     });
   });
 
   describe('createEvent', () => {
-    it('fetches a token, then posts an all-day event and returns the new id', async () => {
+    it('fetches a token from the tenant derived from OIDC_ISSUER_URL, then posts an all-day event', async () => {
       fetchMock
         .mockResolvedValueOnce(
           jsonResponse(200, { access_token: 'tok-1', expires_in: 3600 }),
@@ -54,10 +60,15 @@ describe('GraphClientService', () => {
 
       expect(result).toBe('graph-event-1');
       expect(fetchMock).toHaveBeenCalledTimes(2);
-      const [tokenUrl] = fetchMock.mock.calls[0] as [string];
+      const [tokenUrl, tokenInit] = fetchMock.mock.calls[0] as [
+        string,
+        { body: URLSearchParams },
+      ];
       expect(tokenUrl).toBe(
         'https://login.microsoftonline.com/tenant-1/oauth2/v2.0/token',
       );
+      expect(tokenInit.body.get('client_id')).toBe('client-1');
+      expect(tokenInit.body.get('client_secret')).toBe('secret-1');
       const [eventUrl, eventInit] = fetchMock.mock.calls[1] as [
         string,
         { headers: Record<string, string>; body: string },

ApiCore-Backend/src/calendar-sync/graph-client.service.ts

@@ -27,15 +27,34 @@ function getErrorMessage(error: unknown): string {
   return error instanceof Error ? error.message : String(error);
 }
 
+// Reuses the same Entra app registration as interactive SSO login
+// (OIDC_ISSUER_URL/OIDC_CLIENT_ID/OIDC_CLIENT_SECRET) for the app-only
+// Graph client-credentials flow, instead of a second, separate app
+// registration - one enterprise application covers both, as long as it
+// also has the "Calendars.ReadWrite" Application permission (admin-
+// consented) alongside its delegated login scopes. OIDC_ISSUER_URL is
+// "https://login.microsoftonline.com/<tenant-id>/v2.0" - the tenant id is
+// its first path segment.
+function tenantIdFromIssuerUrl(issuerUrl: string): string | null {
+  try {
+    const segments = new URL(issuerUrl).pathname.split('/').filter(Boolean);
+    return segments[0] ?? null;
+  } catch {
+    return null;
+  }
+}
+
 @Injectable()
 export class GraphClientService {
   private cachedToken: CachedToken | null = null;
 
   isConfigured(): boolean {
+    const issuerUrl = process.env.OIDC_ISSUER_URL;
     return Boolean(
-      process.env.M365_CALENDAR_TENANT_ID &&
-      process.env.M365_CALENDAR_CLIENT_ID &&
-      process.env.M365_CALENDAR_CLIENT_SECRET,
+      issuerUrl &&
+      tenantIdFromIssuerUrl(issuerUrl) &&
+      process.env.OIDC_CLIENT_ID &&
+      process.env.OIDC_CLIENT_SECRET,
     );
   }
 
@@ -44,12 +63,13 @@ export class GraphClientService {
       return this.cachedToken.accessToken;
     }
 
-    const tenantId = process.env.M365_CALENDAR_TENANT_ID;
-    const clientId = process.env.M365_CALENDAR_CLIENT_ID;
-    const clientSecret = process.env.M365_CALENDAR_CLIENT_SECRET;
+    const issuerUrl = process.env.OIDC_ISSUER_URL;
+    const clientId = process.env.OIDC_CLIENT_ID;
+    const clientSecret = process.env.OIDC_CLIENT_SECRET;
+    const tenantId = issuerUrl ? tenantIdFromIssuerUrl(issuerUrl) : null;
     if (!tenantId || !clientId || !clientSecret) {
       throw new Error(
-        'M365-Kalender-Synchronisation ist nicht konfiguriert (Env-Variablen fehlen)',
+        'M365-Kalender-Synchronisation ist nicht konfiguriert (SSO-Env-Variablen fehlen)',
       );
     }