Guards

cmdkit/contrib/guards.py

@@ -0,0 +1,67 @@
+# SPDX-FileCopyrightText: 2021 CmdKit Developers
+# SPDX-License-Identifier: Apache-2.0
+
+"""
+Guarded execution Provider. The decorator based provider extends functionality by allowing
+the safe and symantically simple support for guarded execution of applications(groups).
+
+TODO:
+    - unit testing
+    - doctests and examples
+    - add more guards as needed
+"""
+
+# type annotations
+from __future__ import annotations
+from typing import cast, Any, Callable, Optional, TypeVar, Union
+from collections.abc import Container
+
+# system libraries
+import os
+import grp
+import logging
+from functools import wraps
+
+# static analysis
+F = TypeVar('F', bound = Callable[..., Any])
+D = Callable[[F], F]
+
+logger = logging.getLogger(__name__)
+
+class AuthError(Exception):
+    """Raised when cannot authenticate user."""
+
+class LibraryError(Exception):
+    """Raised when handling errors raised by library or support modules."""
+
+def authorized(*, groups: Optional[Union[str, Container[str]]] = None,
+               message: str = 'User does not have permissions for this command!',
+               root: Optional[bool] = None, users: Optional[Union[str, Container[str]]] = None) -> D:
+    """Decorator which assures that only allowed users may execute the decorated funtion; this is based on 
+    checking the executing process against a number of optional criteria. The various options (e.g., groups and users) 
+    represent intersection operators, while the collection within an option represent union operators."""
+    def decorator(function: F) -> F:
+        @wraps(function)
+        def wrapper(*args, **kwargs):
+            try:
+                if root is not None:
+                    assert os.geteuid() == 0 if root else os.geteuid() != 0
+                if users is not None:
+                    if isinstance(users, str):
+                        assert os.getlogin() == users
+                    else:
+                        assert os.getlogin() in users
+                if groups is not None:
+                    if isinstance(groups, str):
+                        assert grp.getgrnam(groups).gr_gid in os.getgroups()
+                    else:
+                        assert any(grp.getgrnam(g).gr_gid in os.getgroups() for g in groups)
+            except AssertionError:
+                raise AuthError(message)
+            except KeyError:
+                raise LibraryError(f'Group <{group}> not found in system groups!')
+            logger.debug(f'authorized -- Guarded a call into <{function.__name__}>.')
+            return function(*args, **kwargs)
+        return cast(F, wrapper)
+    return decorator
+