Ensure public access is disabled for Amazon Simple Notification Service (SNS)

Allowing unrestricted, public access to cloud services could open an application up to external attack. Disallowing this access is typically considered best practice.

In AWS Console -

1. Sign in to the AWS console and go to the SNS console.
2. In the Navigation pane, select Topics.
3. In the list of Topics, select the Topic to edit.
4. Expand the Access section, and then edit the policy.
5. Select Save changes.

In Terraform -

1. Review the policy attached to the aws_sns_topic resource and ensure necessary changes are made.

References:
https://docs.aws.amazon.com/sns/latest/dg/sns-access-policy-use-cases.html
https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/sns_topic