Issue #198: only warn about file permissions on windows

`os.chmod` does not change group/other permission on Windows,
so not useful to fail on that at the moment.

Author: soxofaan

CHANGELOG.md

@@ -10,6 +10,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changed
 
+- Improve OpenID Connect usability on Windows: don't raise exception on file permissions 
+  that can not be changed (by `os.chmod` on Windows) ([#198](https://github.com/Open-EO/openeo-python-client/issues/198))
+
 ### Removed
 
 ### Fixed

openeo/rest/auth/config.py

@@ -8,7 +8,9 @@
 
 import json
 import logging
+import platform
 import stat
+import warnings
 from datetime import datetime
 from pathlib import Path
 from typing import Union, Tuple, Dict
@@ -25,10 +27,13 @@ def assert_private_file(path: Path):
     """Check that given file is only readable by user."""
     mode = path.stat().st_mode
     if (mode & stat.S_IRWXG) or (mode & stat.S_IRWXO):
-        raise PermissionError(
-            "File {p} is readable by others: st_mode {a:o} (expected permissions: {e:o}).".format(
-                p=path, a=mode, e=_PRIVATE_PERMS)
+        message = "File {p} could be readable by others: mode {a:o} (expected: {e:o}).".format(
+            p=path, a=mode & (stat.S_IRWXU | stat.S_IRWXG | stat.S_IRWXO), e=_PRIVATE_PERMS
         )
+        if platform.system() == 'Windows':
+            warnings.warn(message)
+        else:
+            raise PermissionError(message)
 
 
 def utcnow_rfc3339() -> str:

tests/rest/auth/test_config.py

@@ -39,9 +39,9 @@ def test_wrong_permissions(self, tmp_path):
         with private.path.open("w") as f:
             json.dump({"foo": "bar"}, f)
         assert private.path.stat().st_mode & 0o077 > 0
-        with pytest.raises(PermissionError, match="readable by others.*expected permissions: 600"):
+        with pytest.raises(PermissionError, match="readable by others.*expected: 600"):
             private.get("foo")
-        with pytest.raises(PermissionError, match="readable by others.*expected permissions: 600"):
+        with pytest.raises(PermissionError, match="readable by others.*expected: 600"):
             private.set("foo", value="lol")
 
     def test_set_get(self, tmp_path):
@@ -130,9 +130,9 @@ def test_public_file(self, tmp_path):
         with path.open("w") as f:
             json.dump({}, f)
         r = RefreshTokenStore(path=path)
-        with pytest.raises(PermissionError, match="readable by others.*expected permissions: 600"):
+        with pytest.raises(PermissionError, match="readable by others.*expected: 600"):
             r.get_refresh_token("foo", "bar")
-        with pytest.raises(PermissionError, match="readable by others.*expected permissions: 600"):
+        with pytest.raises(PermissionError, match="readable by others.*expected: 600"):
             r.set_refresh_token("foo", "bar", "imd6$3cr3t")
 
     def test_permissions(self, tmp_path):