Add optional param for AWS IAM role assumption

[hhamalai]

Fixes #142

Proposed Changes

• add flag to specify role arn
• if role arn is specified, use access keys to assume the role with arn provided

Description

Allows specifying role ARN which, if specified, is assumed with STS. All S3 operations are executed with this role.

Checklist

• Read the CONTRIBUTING document.
• Read the CODE OF CONDUCT document.
• Ensure your code follows the code style of this project.
• Ensure CI and all other PR checks are green OR
  • Code compiles correctly.
  • Created tests which fail without the change (if possible).
  • All new and existing tests passed.
• Add your changes to Unreleased section of CHANGELOG.
• Improve and update the README (if necessary).

[kakkoyun]

Looking good. Thanks a lot for the contribution.

Is there way to test thing with our setup? We have minio, it'd be good to have tests.

[hhamalai]

Is there way to test thing with our setup? We have minio, it'd be good to have tests.

I didn't see any authentication related tests in the code, at least for AWS. What's your take on mocked unit tests, that would be plausible, but now when thinking about it, I can also check the minio support for role assumption as documented here https://github.com/minio/minio/blob/master/docs/sts/assume-role.md

[kakkoyun]

@hhamalai
We have rudimentary happy path tests in the form of high-level e2e tests in here

drone-cache/internal/plugin/plugin_test.go

Line 386 in c6fa146

func setupS3(t *testing.T, c *Config, name string) {

What we can either extend those or even better add a specific case in here https://github.com/meltwater/drone-cache/blob/master/storage/backend/s3/s3_test.go

Even a simple one to prevent regressions would suffice.

[hhamalai]

Hi, I added the test case, unfortunately it required quite a bit of too many changes. I am still not too familiar with minio, so take the following findings with a grain of salt:

1. need newer version minio in order to support STS operations
2. need a creation of users an policies on minio as the admin user cannot use STS (in docker-compose & drone yaml)

[kakkoyun]

Wow, what a great PR! Thank you very much for this contribution and level of code quality.

It looks good to me. I have only requested a single change concerning package imports. If you can fix it I'll merge this immediately.