Testing if webdav directory WRITABLE with SharpBox API

Question

I am trying to list files and directories in webdav for users, i want to test if directory is writable using Sharpbox.

Storage.Open(DavConfig, cred);
rootFolder = Storage.GetFolder(dir);
foreach (var file in rootFolder)
        {
            Boolean valid = false;
            Boolean IsDirectory = file is ICloudDirectoryEntry;
            if (IsDirectory)
            {
                valid = true;
            }
            else
            {
                valid = file.Name.Contains(".");
            }

            if (valid) {
                string filePath = basePath + file.Name;
                DavFile davfile = new DavFile(filePath, file.Name, file.Length, file.Modified, IsDirectory);
                Files.Add(davfile);
            }

        }

if the Entry is directory, how to check if it is writable ?