gcloud beta terraform vet quickstart

This quickstart shows you how to apply a constraint that enforces a domain restriction. You'll test that constraint and intentionally throw an error. Then you'll modify the constraint so that your domain passes.

Before you begin

You need a Google Cloud project.
You need the following Identity and Access Management (IAM) permissions for that project:
- resourcemanager.projects.getIamPolicy – This permission can be granted with the Security Reviewer role for the organization.
- resourcemanager.projects.get – This permission can be granted with the Project Viewer role for the organization.

To get you started quickly, these instructions use a Cloud Shell that's pre-installed with Terraform, and with a cloned Policy Library repository. The instructions assume you already have a Google Cloud account.

Quickstart

Go to the Cloud Shell and clone the policy library.

Clone policy library
Copy the sample IAM domain restriction constraint into the policies/constraints directory.
```
cp samples/iam_service_accounts_only.yaml policies/constraints
```

Examine the constraint you copied by printing it to the terminal.

cat policies/constraints/iam_service_accounts_only.yaml

The output looks like this:

# This constraint checks that all IAM policy members are in the
# "gserviceaccount.com" domain.
apiVersion: constraints.gatekeeper.sh/v1alpha1
kind: GCPIAMAllowedPolicyMemberDomainsConstraintV2
metadata:
  name: service_accounts_only
  annotations:
    description: Checks that members that have been granted IAM roles belong to allowlisted
      domains.
spec:
  severity: high
  match:
    target: # {"$ref":"#/definitions/io.k8s.cli.setters.target"}
    - "organizations/**"
  parameters:
    domains:
    - gserviceaccount.com

Notice gserviceaccount.com at the bottom. This specifies that only members from the gserviceaccount.com domain can be present in an IAM policy.

To verify that the policy works as expected, create the following Terraform main.tf file in the current directory. You can use nano, vim, or the Cloud Shell Editor to create policy-library/main.tf.
```
terraform {
  required_providers {
    google = {
      source = "hashicorp/google"
      version = "~> 3.84"
    }
  }
}

resource "google_project_iam_binding" "sample_iam_binding" {
  project = "PROJECT_ID"
  role    = "roles/viewer"

  members = [
    "user:EMAIL_ADDRESS"
  ]
}
```
Replace the following:
- PROJECT_ID: your project ID.
- EMAIL_ADDRESS: a sample email address. This can be any valid email address. For example, user@example.com.
Initialize Terraform and generate a Terraform plan using the following:
```
terraform init
```
Export the Terraform plan, if asked, click Authorize when prompted:
```
terraform plan -out=test.tfplan
```

Convert the Terraform plan to JSON:

terraform show -json ./test.tfplan > ./tfplan.json

Install the terraform-tools component:

sudo apt-get install google-cloud-sdk-terraform-tools

Enter the following command to validate that your Terraform plan complies with your policies:

gcloud beta terraform vet tfplan.json --policy-library=. --format=json

Since the email address you provided in the IAM policy binding does not belong to a service account, the plan violates the constraint you set up.

[
{
  "constraint": "GCPIAMAllowedPolicyMemberDomainsConstraintV2.service_accounts_only",
  "constraint_config": {
    "api_version": "constraints.gatekeeper.sh/v1alpha1",
    "kind": "GCPIAMAllowedPolicyMemberDomainsConstraintV2",
    "metadata": {
      "annotations": {
        "description": "Checks that members that have been granted IAM roles belong to allowlisted domains.",
        "validation.gcp.forsetisecurity.org/originalName": "service_accounts_only",
        "validation.gcp.forsetisecurity.org/yamlpath": "policies/constraints/iam_service_accounts_only.yaml"
      },
      "name": "service-accounts-only"
    },
    "spec": {
      "match": {
        "target": [
          "organizations/**"
        ]
      },
      "parameters": {
        "domains": [
          "gserviceaccount.com"
        ]
      },
      "severity": "high"
    }
  },
  "message": "IAM policy for //cloudresourcemanager.googleapis.com/projects/PROJECT_ID contains member from unexpected domain: user:user@example.com",
  "metadata": {
    "ancestry_path": "organizations/ORG_ID/projects/PROJECT_ID",
    "constraint": {
      "annotations": {
        "description": "Checks that members that have been granted IAM roles belong to allowlisted domains.",
        "validation.gcp.forsetisecurity.org/originalName": "service_accounts_only",
        "validation.gcp.forsetisecurity.org/yamlpath": "policies/constraints/iam_service_accounts_only.yaml"
      },
      "labels": {},
      "parameters": {
        "domains": [
          "gserviceaccount.com"
        ]
      }
    },
    "details": {
      "member": "user:user@example.com",
      "resource": "//cloudresourcemanager.googleapis.com/projects/PROJECT_ID"
    }
  },
  "resource": "//cloudresourcemanager.googleapis.com/projects/PROJECT_ID",
  "severity": "high"
}
]

To allow another domain (your email), edit policy-library/policies/constraints/iam_service_accounts_only.yaml and append your email domain to the domains allowlist. In the following example, we've added example.com, but you'd enter the domain for your own email address:

apiVersion: constraints.gatekeeper.sh/v1alpha1
kind: GCPIAMAllowedPolicyMemberDomainsConstraintV1
metadata:
  name: service_accounts_only
spec:
  severity: high
  match:
    target: ["organizations/**"]
  parameters:
    domains:
      - gserviceaccount.com
      - example.com

Now validate your Terraform plan again, and this should result in no violations found:
```
gcloud beta terraform vet tfplan.json --policy-library=. --format=json
```
Expected output:
```
[]
```

Troubleshooting

If you receive the following error, "Error 403: The caller does not have permission, forbidden", then you either didn't replace PROJECT_ID in policy-library/main.tf with the name of your project, or you don't have the necessary permissions on the project you specified.

After editing the project name and/or permissions (resourcemanager.projects.getIamPolicy and resourcemanager.projects.get), go back and export the Terraform plan again, and then convert the Terraform plan to JSON.