Implement sync with a Dropbox App

[louisabraham]

To solve the issues I got in #123, I created a Dropbox App that syncs an app folder using the official API.

The user gets the authorization token by clicking on the following link that is included in the README: https://www.dropbox.com/oauth2/authorize?client_id=5oyw72cfwcp352f&response_type=token&redirect_uri=https://louisabraham.github.io/KoboCloud

The workflow redirects to a static page (https://louisabraham.github.io/KoboCloud) displaying the token for the user and this page is contained in /docs.

This authorization token is limited to reading the files in the app folder.

If more than 500 people use that app, it will need to be approved by Dropbox as an official Dropbox app. Even if they were to refuse, it would be easy to recreate the same, and simply change the client_id in the authorization link.

Steps to create such an app:

• go to https://www.dropbox.com/developers/apps
• create an app, they are calling it "Scoped App (App Folder)" right now
• give permission files.content.read
• select "No expiration" for "Access token expiration"
• allow the URL of the static page (https://louisabraham.github.io/KoboCloud) as a redirect URL
• replace 5oyw72cfwcp352f with the "App key" in the link above

I tested and it works flawlessly for me. I cannot provide testcases since it does not support public links.

[louisabraham]

Hi, the check that fails is unrelated to my PR. It is a gdrive 403 error.

[fsantini]

Hi, the check that fails is unrelated to my PR. It is a gdrive 403 error.

Yeah, saw that. Thanks for your contribution. I was afraid it would be much more disruptive, but you did a good job. Let me review the PR thoroughly and I'll merge it.

[louisabraham]

The only commit that could be disruptive is https://github.com/fsantini/KoboCloud/pull/124/commits/19e5f249eada16cabfb1d6f6d279a22fb15dafc9

But it should actually improve things!