docs: docblock for getChildForPrincipal class

Signed-off-by: Josh <josh.t.richards@gmail.com>

lib/DAV/RootCollection.php

@@ -11,9 +11,15 @@
 use OCA\GroupFolders\Folder\FolderManager;
 use OCP\Files\IRootFolder;
 use OCP\IUserSession;
+use Sabre\DAV\Exception\Forbidden;
 use Sabre\DAVACL\AbstractPrincipalCollection;
 use Sabre\DAVACL\PrincipalBackend;
 
+/**
+ * WebDAV root collection for the GroupFolders app.
+ *
+ * Provides access to user principal nodes representing each user's group folders home.
+ */
 class RootCollection extends AbstractPrincipalCollection {
 	public function __construct(
 		private readonly IUserSession $userSession,
@@ -25,17 +31,20 @@ public function __construct(
 	}
 
 	/**
-	 * This method returns a node for a principal.
+	 * Returns a GroupFoldersHome for the principal if the authenticated user matches.
 	 *
 	 * The passed array contains principal information, and is guaranteed to
 	 * at least contain a uri item. Other properties may or may not be
 	 * supplied by the authentication backend.
+	 *
+	 * @throws \Sabre\DAV\Exception\Forbidden If the principal does not match the currently logged-in user.
 	 */
 	public function getChildForPrincipal(array $principalInfo): GroupFoldersHome {
 		[, $name] = \Sabre\Uri\split($principalInfo['uri']);
 		$user = $this->userSession->getUser();
+
 		if (is_null($user) || $name !== $user->getUID()) {
-			throw new \Sabre\DAV\Exception\Forbidden();
+			throw new Forbidden('Access to this groupfolders principal is not allowed for this user.');
 		}
 
 		return new GroupFoldersHome($principalInfo, $this->folderManager, $this->rootFolder, $user);