Add authenticated finance REST API

app/api/auth.py

@@ -0,0 +1,16 @@
+import os
+import secrets
+from typing import Annotated
+from fastapi import Depends, HTTPException
+from fastapi.security import HTTPAuthorizationCredentials, HTTPBearer
+
+bearer = HTTPBearer(auto_error=False, scheme_name='FinanceAPIToken',
+                    description='Bearer-Token aus FINANCE_API_TOKEN. Kein Standard-Token.')
+
+
+def require_token(credentials: Annotated[HTTPAuthorizationCredentials | None, Depends(bearer)]):
+    token = os.environ.get('FINANCE_API_TOKEN', '')
+    if not token.strip() or token == 'change-me':
+        raise HTTPException(503, 'API nicht konfiguriert. FINANCE_API_TOKEN muss gesetzt werden.')
+    if credentials is None or not secrets.compare_digest(credentials.credentials.encode(), token.encode()):
+        raise HTTPException(401, 'Fehlendes oder ungültiges API-Token.', headers={'WWW-Authenticate': 'Bearer'})