Implement using group calenders.

Based on the ldap groups the user is member of group calender usage is implemented.
The group calenders must be placed in the GROUPS directory based under collection_root_folder.
The name of the group calender directory is the base64 encoded name of the group to avoid trouble with spaces and special characters in name.
If the directory does not exist the group will be ignored.

radicale/app/propfind.py

@@ -392,7 +392,8 @@ class ApplicationPartPropfind(ApplicationBase):
             return httputils.REQUEST_TIMEOUT
         with self._storage.acquire_lock("r", user):
             items_iter = iter(self._storage.discover(
-                path, environ.get("HTTP_DEPTH", "0")))
+                path, environ.get("HTTP_DEPTH", "0"),
+                None, self._rights._user_groups))
             # take root item for rights checking
             item = next(items_iter, None)
             if not item:

radicale/storage/multifilesystem/discover.py

@@ -18,6 +18,7 @@
 
 import os
 import posixpath
+import base64
 from typing import Callable, ContextManager, Iterator, Optional, cast
 
 from radicale import pathutils, types
@@ -36,7 +37,8 @@ class StoragePartDiscover(StorageBase):
 
     def discover(
             self, path: str, depth: str = "0", child_context_manager: Optional[
-                Callable[[str, Optional[str]], ContextManager[None]]] = None
+                Callable[[str, Optional[str]], ContextManager[None]]] = None,
+                user_groups: Set[str] = set([])
             ) -> Iterator[types.CollectionOrItem]:
         # assert isinstance(self, multifilesystem.Storage)
         if child_context_manager is None:
@@ -102,3 +104,13 @@ class StoragePartDiscover(StorageBase):
             with child_context_manager(sane_child_path, None):
                 yield self._collection_class(
                     cast(multifilesystem.Storage, self), child_path)
+        for group in user_groups:
+            href = base64.b64encode(group.encode('utf-8')).decode('ascii')
+            logger.debug(f"searching for group calendar {group} {href}")
+            sane_child_path = f"GROUPS/{href}"
+            if not os.path.isdir(pathutils.path_to_filesystem(folder, sane_child_path)):
+                continue
+            child_path = f"/GROUPS/{href}/"
+            with child_context_manager(sane_child_path, None):
+                yield self._collection_class(
+                    cast(multifilesystem.Storage, self), child_path)