[Enhancement]: Emit warnings on IAM policy creation when duplicate keys are configured

[breathingdust]

Description

This enhancement proposal stems from this issue raised in Terraform Core where values in a map object can be squashed when duplicate keys are supplied. See the linked issue for a detailed discussion of the root causes and proposed solutions at the core level.

In the AWS provider we could potentially emit warnings when an IAM policy is configured with duplicate Condition keys, either within a raw JSON string or via the condition block of an aws_iam_policy_document data source. Because this scenario could lead to an overly permissive policy under certain conditions, these arguably these should be errors, but introducing errors would constitute a breaking change. We may introduce warnings at this time, and move to errors in the next major version.

This would need to be performed both on on the raw string as input for the aws_iam_role / aws_iam_policy / aws_iam_role_policy resources, as well as the more structured input of the aws_iam_policy_document. If the practitioner has used jsonencode() in their configuration, then the input would have already been squashed by the time the provider sees it, and no warning will be possible.

This behavior should also be thoroughly documented in the respective registry documentation, and potentially in the Developer Guide.

Affected Resource(s) and/or Data Source(s)

• aws_iam_role
• aws_iam_policy
• aws_iam_policy_document
• aws_iam_role_policy

Potential Terraform Configuration

No response

References

• Warning on Duplicate keys in a map object.  terraform#28727

Would you like to implement a fix?

None

[github-actions]

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[github-actions]

This functionality has been released in v5.19.0 of the Terraform AWS Provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

For further feature requests or bug reports with this functionality, please create a new GitHub issue following the template. Thank you!

[github-actions]

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