[kovidgoyal]

write actions are dangerous. I am absolutely not willing to open write actions to un-authenticated users. Sure in your particular use case, its fine because you have moved authentication out of the content server. But in general if it were possible to allow un-auth write then people would do it, and one of those un-auth write servers would get all its books deleted by some mischevious person and then I'd have to deal with angry posts along the lines of "calibre ate all my books".