fix: authorize every path an operation touches

Recursive COPY, MOVE, DELETE and PROPFIND were checked only against the
requested path, reaching descendants their rules deny. A broad rule shadowed
a narrower one naming a collection. LOCK was allowed on any permission, so a
read-only user could create files and block writers. Rules compared case
where the backing file system does not.

README.md

@@ -119,6 +119,8 @@ directory: /data
 # The default permissions for users. This is a case insensitive option. Possible
 # permissions: C (Create), R (Read), U (Update), D (Delete). You can combine multiple
 # permissions. For example, to allow to read and create, set "RC". Default is "R".
+# LOCK counts as a write: it needs U on a path that exists and C on one that does
+# not, since locking a path that does not exist creates it.
 permissions: R
 
 # The default permissions rules for users. Default is none. Rules are applied
@@ -240,6 +242,10 @@ A `path` rule is a prefix match. A rule written with a trailing slash also cover
 
 A `regex` rule is matched literally against the path, and gets none of the above handling. In particular `regex: "^/secret/"` does **not** match a request for `/secret` itself. Write `regex: "^/secret(/|$)"` if you want to cover the collection too.
 
+Rules apply to every path an operation touches, not only the one it names. Collection listings leave out entries the rules deny, copying a collection leaves those entries behind, and a `MOVE` or `DELETE` that would act on a denied descendant is refused outright.
+
+Rules follow the case sensitivity of the file system, which each served directory is probed for at startup. Where names are case-insensitive, as on APFS and NTFS, `path: /secret/` also covers `/SECRET/`, a `regex` is matched against the folded path as well as the path as written, and Unicode normal forms count as one name. Elsewhere rules are matched exactly, since `/secret` and `/SECRET` are then different directories.
+
 ### CORS
 
 The `allowed_*` properties are optional, the default value for each of them will be `*`. `exposed_headers` is optional as well, but is not set if not defined. Setting `allow_private_network` to `true` to allow Private-Network-Access preflight requests. Setting `credentials` to `true` will allow you to: