Allow TokenUser class to be configurable

[ajhodges]

Addresses #171 , adding a setting TOKEN_USER_CLASS, that can be used to override the default TokenUser. Added a unit test to ensure that this works, and there's an existing assertion that the default TokenUser class is preserved in TestJWTTokenUserAuthentication.test_get_user.

[ajhodges]

Also pretty please requesting a new release if/when this gets merged :)

[KimSoungRyoul]

it would be required feature

This way we don't have to override

[ajhodges]

@davesque any feedback on this PR?

[jrsupplee]

Why not just create your own authentication class with a get_user method that returns the desired token?

[ajhodges]

We certainly could make our own authentication class that just uses a different user, but, as shown by this PR, it's also fairly trivial to add support to make this easily configurable via settings. I prefer to not re-write code if I don't need to. It's always a technical-debt-win in my book if I can rely on an externally maintained package vs forking/reimplementing it on my own.

I feel like a setting is appropriate for this, and judging by the ':+1:'s I'm not alone. Is there an issue you have with this solution?

[jvhellemondt]

This would be great. I have the issue that I cannot exclude
'django.contrib.auth', 'django.contrib.contenttypes',

in my settings due to this.

[davesque]

LGTM.