aws_sns_topic_policy

resource:
  aws_sns_topic:
    test:
      name: my-topic-with-policy
  aws_sns_topic_policy:
    custom:
      arn: '${aws_sns_topic.test.arn}'
      policy: "{\n  \"Version\": \"2012-10-17\",\n  \"Id\": \"default\",\n  \"Statement\":[{\n    \"Sid\": \"default\",\n    \"Effect\": \"Allow\",\n    \"Principal\": {\"AWS\":\"*\"},\n    \"Action\": [\n      \"SNS:GetTopicAttributes\",\n      \"SNS:SetTopicAttributes\",\n      \"SNS:AddPermission\",\n      \"SNS:RemovePermission\",\n      \"SNS:DeleteTopic\"\n    ],\n    \"Resource\": \"${aws_sns_topic.test.arn}\"\n  }]\n}"

resource "aws_sns_topic" "test" {
  name = "my-topic-with-policy"
}

resource "aws_sns_topic_policy" "custom" {
  arn = "${aws_sns_topic.test.arn}"
  policy = <<POLICY
{
  "Version": "2012-10-17",
  "Id": "default",
  "Statement":[{
    "Sid": "default",
    "Effect": "Allow",
    "Principal": {"AWS":"*"},
    "Action": [
      "SNS:GetTopicAttributes",
      "SNS:SetTopicAttributes",
      "SNS:AddPermission",
      "SNS:RemovePermission",
      "SNS:DeleteTopic"
    ],
    "Resource": "${aws_sns_topic.test.arn}"
  }]
}
POLICY
}