fix: set policy version appropriately after roleset bindings have changed

[austingebauer]

Overview

Closes #88

This PR ensures that the IAM policy version returned from getIamPolicy is the same one provided to setIamPolicy after bindings have been changed. The version number was not being copied into the new Policy struct when bindings changed, which led to the error:

Error writing data to gcp/roleset/my-key-roleset: Error making API request.

URL: PUT http://127.0.0.1:8200/v1/gcp/roleset/my-key-roleset
Code: 400. Errors:

* unable to set policy: googleapi: Error 400: Specified policy version (1) cannot be less than the existing policy version (3). For more information, please refer to https://cloud.google.com/iam/docs/policies#versions.

I was able to reproduce the issue and verify the change in this PR fixes it.

Related Issues/Pull Requests

• Unable to set policy: Specified policy version (1) cannot be less than the existing policy version (3) #88
• Handle version 3 policies for Resource Manager IAM requests ([projects, folders, organziations].getIamPolicy) #77

Contributor Checklist

• Add relevant docs to upstream Vault repository, or sufficient reasoning why docs won’t be added yet
  • No docs needed for this fix
• Backwards compatible
• Add output for any tests not ran in CI to the PR description (eg, acceptance tests)

=== RUN   TestIamResource_ServiceAccount
--- PASS: TestIamResource_ServiceAccount (2.02s)
PASS

make test
?       github.com/hashicorp/vault-plugin-secrets-gcp   [no test files]
ok      github.com/hashicorp/vault-plugin-secrets-gcp/plugin    (cached)
ok      github.com/hashicorp/vault-plugin-secrets-gcp/plugin/iamutil    0.315s
?       github.com/hashicorp/vault-plugin-secrets-gcp/plugin/iamutil/internal   [no test files]
ok      github.com/hashicorp/vault-plugin-secrets-gcp/plugin/util       (cached)
?       github.com/hashicorp/vault-plugin-secrets-gcp/scripts/gohelpers [no test files]

[somethingnew2-0]

Thank you for fixing this! 🥳