Ai Terraform Plan Review: Plan Diff Gates Before Any Apply Runs

# modules/ai_gate/main.tf — illustrative boundaries
resource "aws_iam_policy" "svc" {
  name   = var.policy_name
  policy = data.aws_iam_policy_document.svc.json
}

# ❌ Agent anti-pattern
# resource "aws_iam_policy" "svc" {
#   policy = jsonencode({
#     Statement = [{ Effect = "Allow", Action = "*", Resource = "*" }]
#   })
# }

# ci/terraform-agent-pr.sh
set -euo pipefail
terraform init -backend-config=backend.hcl
terraform plan -input=false -out=tfplan.bin
terraform show -json tfplan.bin > tfplan.json

# ✅ OPA on the plan, not on HCL text alone
conftest test tfplan.json -p policy/terraform

# ❌ terraform apply in the agent tool allowlist

# policy/terraform/no_wildcards.rego
package terraform.aws

deny[msg] {
  some change in input.resource_changes
  change.type == "aws_iam_policy"
  after := change.change.after
  contains(after.policy, `"Action":"*"`)
  msg := sprintf("wildcard Action in %s", [change.address])
}

deny[msg] {
  some change in input.resource_changes
  change.type == "aws_security_group_rule"
  change.change.after.cidr_blocks[_] == "0.0.0.0/0"
  change.change.after.to_port == 22
  msg := "SSH open to world"
}

deny[msg] {
  some change in input.resource_changes
  change.type == "aws_kms_key"
  change.change.actions[_] == "delete"
  msg := "KMS key deletion requires break-glass label"
}

# .github/workflows/tf-agent.yml
jobs:
  plan:
    if: contains(github.event.pull_request.labels.*.name, 'ai-terraform')
    steps:
      - run: ./ci/terraform-agent-pr.sh
      - uses: actions/upload-artifact@v4
        with: { name: tfplan, path: tfplan.bin }
  apply:
    needs: plan
    environment: production-terraform  # ✅ GitHub env protection rules
    if: github.event.review.state == 'approved'
    steps:
      - run: terraform apply -input=false tfplan.bin