allow to override settings at run time

[millerthegorilla]

Feature Request

the settings to django storages can be overridden at run time, which can be useful, for example, if I am using the dropbox backend.

Currently the dropbox storage backend works fine with a long term o-auth token, but according to the info on the dropbox app site, long term oauth tokens are going to be deprecated in the future. One can then obtain a short lived token using the dropbox python api to query the endpoint /token/from_oauth1 wrapping your secret key etc which then returns an oauth2 short lived access code for use by your app.

If I were using the django-storage code raw I could handle this by overriding the call to the class DropBoxStorage, I think, as I haven't tested it personally, but I do know that I can not override django-dbbackup in any way to change the oauth token setting at runtime, so I can not use short lived token access.

Is your feature request related to a problem?

Long lived o-auth2 access tokens are to be deprecated in the future, according to the Dropbox app info.

Describe the solution you'd like

I would like to see some code written that would allow me to adjust the value of the oauth2 token at runtime, or, better still, pass the necessary settings to django_dbbackup to allow the retrieval and use of a short-lived oauth2 token.

Additional context

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PR link

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