Refresh Token Reuse Protection

[soerface]

Fixes#1404

Description of the Change

This PR adds a new setting / feature REFRESH_TOKEN_REUSE_PROTECTION. It allows django-oauth-toolkit to revoke related refresh and access tokens whenever an already revoked refresh token is used again. This indicates a breach - for details see #1404.

The implementation does it by adding a new column token_family to the refresh token table. When a new refresh token is created with an existing refresh token, the new refresh token get's assigned the same token_family value as the original token. This ensures that all tokens from the same session share the same family. Otherwise (first token of a session, gathered by e.g. username & password), the token_family is a random value.

Whenever a revoked refresh token is presented, the server will query for all tokens with the same token_family value, and call the .revoke() method on it.

To discuss: The "select all tokens of a family and revoke" code is always being run when a revoked token is presented. Maybe this could provide a vector for a denial of service attack. Therefore, I was wondering if we should set the token_family value to NULL after the whole family has been revoked. Another thought to ease database load was furthermore to use objects.filter(...).delete(), however I was afraid that the logic inside the .revoke() method was relevant and shouldn't be skipped lightheartedly. Furthermore, do you think an index on that new column would be required?

Checklist

• PR only contains one change (considered splitting up PR)
• unit-test added
• documentation updated
• CHANGELOG.md updated (only for user relevant changes)
• author name in AUTHORS

[n2ygk]

@soerface This is a really nice security improvement by following the newer BCPs. I agree that the default for now has to be False to avoid immediate breakage for existing users. We can perhaps raise a DeprecationWarning and eventually make the default be True for a future major release.

I have some questions about the migrations and whether they need migrations.swappable_dependency added to them. I'm stumped by this swappable stuff and you can see there are a number of issues raised over the years by people trying to use the functionality....