Update admin config

docs/desktop/admin-config.mdx

@@ -43,9 +43,54 @@ cryptomator.pluginDir=@{userhome}/cryptomator/plugins
 :::warning
 After creating/editing the file, ensure correct file access permissions!
 
-We recommend read access for all users, **write access only for system/device admins**.
+We recommend read access for all users, **write access only for system/device admins**. On Windows, Cryptomator enforces this and ignores the file otherwise, see [File Permissions on Windows](#file-permissions-on-windows).
 :::
 
+## File Permissions on Windows {/* #file-permissions-on-windows */}
+
+Since Cryptomator 1.19.5, the admin configuration is **only loaded on Windows if it cannot be edited by standard users**. Cryptomator checks the following requirements on every start and ignores the admin configuration if any of them is not met:
+
+* `config.properties`, its directory and all parent directories up to the drive root are owned by `SYSTEM`, `Administrators` or `TrustedInstaller`.
+* No other user or group has permissions to modify the file (meaning write, append, delete, change permissions, take ownership) or to delete or replace one of the directories (delete, delete subfolders and files, change permissions, take ownership). Permissions to create new files in a directory are fine.
+* The path does not contain junctions or symbolic links.
+
+If the admin configuration is ignored, the application log contains a warning starting with `Ignoring admin config`. The warning logged right before it names the concrete cause, e.g. the path and its untrusted owner, the modifying rights granted to an untrusted principal, or the link a path element resolves to.
+
+During installation (including repair and upgrade) the installer sets up the directory `C:\ProgramData\Cryptomator` and, if no admin config exists, places an empty `config.properties` with correct permissions inside it.
+
+An existing `config.properties` is left untouched, **including its owner and permissions**. To replace it with one the installer creates, proceed as follows with elevated privileges:
+
+1. Rename `C:\ProgramData\Cryptomator\config.properties`, e.g. to `config.properties.old`.
+2. Repair the installation, e.g. by running the Cryptomator installer again and choosing *Repair*. This secures the directory and places a new, empty `config.properties` with correct permissions inside it.
+3. Copy the entries you need from the renamed file into the new `config.properties` and delete the renamed file afterwards.
+
+:::warning
+Before copying entries, review the content of the renamed file for unexpected values, especially `cryptomator.pluginDir`.
+:::
+
+For verification, run the following commands in PowerShell:
+
+```powershell
+(Get-Acl "C:\ProgramData\Cryptomator").Sddl
+(Get-Acl "C:\ProgramData\Cryptomator\config.properties").Sddl
+```
+
+Each command prints owner and permissions in [SDDL](https://learn.microsoft.com/en-us/windows/win32/secauthz/security-descriptor-definition-language) form. For a configuration created by the installer, the output is:
+
+```
+O:BAG:SYD:PAI(A;OICI;FA;;;SY)(A;OICI;FA;;;BA)(A;OICI;0x1200a9;;;BU)
+O:SYG:SYD:AI(A;ID;0x1200a9;;;BU)(A;ID;FA;;;BA)(A;ID;FA;;;SY)
+```
+
+`SY` stands for `SYSTEM`, `BA` for `Administrators` and `BU` for `Users`; `TrustedInstaller` has no abbreviation and appears as its full SID. `FA` grants full access, `0x1200a9` read and execute. The installer-generated defaults have the following characteristics:
+
+* The owner (`O:`) is `SY`, `BA` or `S-1-5-80-956008885-3418522649-1831038044-1853292631-2271478464` (`TrustedInstaller`).
+* The permissions after `D:` consist of exactly three entries, one each for `SY`, `BA` and `BU` (order may differ).
+* The directory's permissions contain the `P` flag (`D:PAI`).
+* The file's entries carry the `ID` flag.
+
+A deployment tool that creates the admin config must meet the ownership, access and link restrictions described above; it does not need to reproduce the installer's ACLs exactly.
+
 ## Configurable Properties {/* #configurable-properties */}
 
 The following property keys are supported.