I want use protected files but I don't want made my users authenticate via october, I have a cas server and I want use it. is it possible?
See https://github.com/octobercms/october/blob/develop/modules/backend/controllers/Files.php. You should be able to use that as a reference to build out your own custom controller with whatever authentication system you want, and then you just create a model class that extends https://github.com/octobercms/october/blob/develop/modules/system/models/File.php#L35 and override the getThumb() and getPath() methods to return the URL to your custom controller and then use your custom file model as the attachOne / attachMany relationship model.
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