allow dropbox backend to work with refresh tokens

[millerthegorilla]

Hi, I am using the django-storages as part of django-dbbackup, and am configuring the dropbox parameters in my settings. Everything works fine as expected, but in the dropbox apps info, it is stated that the long-expiration oauth token will be deprecated in the future.

It looks like, according to the dropbox api, the /token/from_oauth1 endpoint can be used in conjunction with your secret key to return an oauth2 shortlived token to allow a call to dropbox function.

I understand that this project is unfortunately not well supported, so I don't expect any changes, but just wanted to point out the potential necessity of making a change before dropbox drop support for the long lived access tokens.

Mtia

[millerthegorilla]

Actually, I've just been looking at the code, and it may well be possible to use the raw storages code if you are using the django_storages code base exclusively, but the django-dbbackup code doesn't allow for much in the way of customization.