Add logging and exception for access token failure

mail/auth.py

@@ -8,6 +8,10 @@
 logger = logging.getLogger(__name__)
 
 
+class AuthenticationError(Exception):
+    pass
+
+
 class Authenticator(Protocol):
     user: str
 
@@ -66,6 +70,10 @@ def _get_access_token(self):
             logger.info("Token not found in cache")
             result = self.app.acquire_token_for_client(scopes=scopes)
 
+        if "access_token" not in result:
+            logger.info(result)
+            raise AuthenticationError("No access token found")
+
         return result["access_token"]
 
     def _encode_access_string(self, username, access_token):

mail/tests/test_auth.py

@@ -1,10 +1,15 @@
 import base64
+import uuid
 from poplib import POP3_SSL
 from unittest.mock import MagicMock, call, patch
 
 from django.test import SimpleTestCase
 
-from mail.auth import BasicAuthentication, ModernAuthentication
+from mail.auth import (
+    AuthenticationError,
+    BasicAuthentication,
+    ModernAuthentication,
+)
 
 
 class BasicAuthenticationTests(SimpleTestCase):
@@ -128,6 +133,44 @@ def test_authenticates_connection_without_silent_acquisition(self):
             ]
         )
 
+    def test_error_acquiring_access_token(self):
+        pop3conn = MagicMock(spec=POP3_SSL)
+        mock_conn = pop3conn()
+
+        username = "username"
+        client_id = "client_id"
+        client_secret = "client_secret"  # nosec
+        tenant_id = "tenant_id"
+
+        mock_failed_result = {
+            'error': 'invalid_client',
+            'error_description': "AAZZZZ1234567: There was an error",
+            'error_codes': [1234567],
+            'timestamp': '2024-08-27 08:59:54Z',
+            'trace_id': str(uuid.uuid4()),
+            'correlation_id': str(uuid.uuid4()),
+            'error_uri': 'https://login.microsoftonline.com/error?code=1234567',
+        }
+
+        with patch("mail.auth.msal") as mock_msal:
+            mock_ConfidentialClientApplication = mock_msal.ConfidentialClientApplication()
+            mock_acquire_token_silent = mock_ConfidentialClientApplication.acquire_token_silent
+            mock_acquire_token_silent.return_value = mock_failed_result
+
+            auth = ModernAuthentication(
+                username,
+                client_id,
+                client_secret,
+                tenant_id,
+            )
+            with self.assertRaises(AuthenticationError), self.assertLogs(logger='mail.auth', level='INFO') as cm:
+                auth.authenticate(mock_conn)
+
+            self.assertIn(
+                f"INFO:mail.auth:{mock_failed_result}",
+                cm.output,
+            )
+
     def test_equal(self):
         username = "username"
         client_id = "client_id"