Add box support

[abdur-rehman-hatio]

Add Box support at least as an option with Dropbox, since it supports 10GB of free storage.

[vineetchoudhary]

Thanks for the request. Box support is not a small change. Also, free plan has a 250 MB per-file upload limit, and Box also imposes limits on direct/shared link downloads and bandwidth. Supporting it would require too many Box specific handling in AppBox and middleware, including rate limit management on middleware.

Overall, no direct link support and the 250 MB per-file upload limit are the main concerns. Because of these limitations, I'm not really in favor of adding support for Box. However, when I get some time, I'll evaluate it in more detail.