Signed keys for image service

[wildfiremedia]

Body

Summary

Avoid mass resize image attack.

Background & Motivation

If we have set only certain sizes that can be accessed using URLs with parameters, users can change the values at will.

Goals

To prevent mass image resizing attacks, I think we need to implement a signed key for each image using a private string (in the .env file) and a public key (in the URL).

[wildfiremedia]

@ascorbic Could we limit to certain sizes to avoid mass resize attack when using _image service?