Allow role assumption

[mdreem]

Enable AWS role assumption mechanism after logging in with the given credentials. See #151.

[mdreem]

I needed to use the AWS role assumption mechanism after logging in with the given credentials so I have implemented it.
This has been attempted in #151 already, but apparently has been abandoned.

[clarafu]

Sorry for the late review! It looks great, I was wondering if there would be a way to have it use the role ARN in a few specific integrations tests and without it in others? Just so that we can have the integration tests run tests on both using role ARN and without?

[mdreem]

Sorry for the late review! It looks great, I was wondering if there would be a way to have it use the role ARN in a few specific integrations tests and without it in others? Just so that we can have the integration tests run tests on both using role ARN and without?

Thanks for checking it out!
When I tested it locally I actually created two buckets, in order to separate :
One I can only access via the role assumption after using credentials, which only allowed the role-assumption.
Another one which I could only access via credentials.

Then I was curious if it still works in all use-cases, so I just switched the bucket, when I ran the test-suite. But if you think there are some specific tests that are sufficient, I think it would also be possible. I'd just need to define an additional parameter for the bucket using the role-assumption, I guess.

[clarafu]

I think everything here is great already, I'm just going to merge it because its been delayed for so long haha. I was just suggesting the test changes so that we can run the tests once to cover all the cases of using role ARN and without but it's honestly not a big deal! Thanks for the PR!!