BUG: Make windows error warning when writing to keyring cache (#24)

Author: snowman2

msal_requests_auth/cache.py

@@ -3,6 +3,7 @@
 https://msal-python.readthedocs.io/en/latest/#msal.SerializableTokenCache
 """
 import os
+import warnings
 from abc import ABC, abstractmethod
 from pathlib import Path
 from typing import Union
@@ -105,7 +106,18 @@ def write_cache(self) -> None:
         """
         Write cache to keyring if needed.
         """
-        if self.has_state_changed:
+        if not self.has_state_changed:
+            return
+
+        try:
             _import_keyring().set_password(
                 "__msal_requests_auth__", "token", self.serialize()
             )
+        except Exception as error:  # pylint: disable=broad-exception-caught
+            # some windows machines have issues writing to keyring
+            # win32ctypes.pywin32.pywintypes.error: (1783, 'CredWrite', 'The stub received bad data')
+            if getattr(error, "winerror", None) != 1783:
+                raise
+            warnings.warn(
+                f"Token cache skipped due to error writing to keyring. Error: {error}"
+            )

test/test_cache.py

@@ -1,5 +1,7 @@
 from unittest.mock import patch
 
+import pytest
+
 from msal_requests_auth.cache import KeyringTokenCache, SimpleTokenCache
 
 
@@ -89,3 +91,50 @@ def test_keyring_token_cache__deserialize(deserialize_mock, keyring_mock):
     keyring_mock.return_value.get_password.return_value = "TEST"
     KeyringTokenCache()
     deserialize_mock.assert_called_with("TEST")
+
+
+@patch("msal_requests_auth.cache._import_keyring")
+@patch("msal_requests_auth.cache.KeyringTokenCache.serialize")
+def test_keyring_token_cache__write_cache__windows_error(serialize_mock, keyring_mock):
+    class MyException(Exception):
+        def __init__(self, *args, **kwargs) -> None:
+            self.winerror = 1783
+            super().__init__(*args, **kwargs)
+
+    keyring_mock.return_value.set_password.side_effect = MyException
+
+    serialize_mock.return_value = "TEST"
+    keyring_mock.return_value.get_password.return_value = None
+    with KeyringTokenCache() as cache:
+        pass
+    keyring_mock.return_value.get_password.assert_called_with(
+        "__msal_requests_auth__", "token"
+    )
+    keyring_mock.return_value.set_password.assert_not_called()
+    cache.has_state_changed = True
+    with pytest.warns(match="Token cache skipped due to error writing to keyring"):
+        with KeyringTokenCache() as cache:
+            cache.has_state_changed = True
+    keyring_mock.return_value.set_password.assert_called_with(
+        "__msal_requests_auth__", "token", "TEST"
+    )
+
+
+@patch("msal_requests_auth.cache._import_keyring")
+@patch("msal_requests_auth.cache.KeyringTokenCache.serialize")
+def test_keyring_token_cache__write_cache__error(serialize_mock, keyring_mock):
+    keyring_mock.return_value.set_password.side_effect = RuntimeError
+    serialize_mock.return_value = "TEST"
+    keyring_mock.return_value.get_password.return_value = None
+    with KeyringTokenCache() as cache:
+        pass
+    keyring_mock.return_value.get_password.assert_called_with(
+        "__msal_requests_auth__", "token"
+    )
+    keyring_mock.return_value.set_password.assert_not_called()
+    with pytest.raises(RuntimeError):
+        with KeyringTokenCache() as cache:
+            cache.has_state_changed = True
+    keyring_mock.return_value.set_password.assert_called_with(
+        "__msal_requests_auth__", "token", "TEST"
+    )