{
  "$schema": "https://schema.management.azure.com/schemas/2019-08-01/managementGroupDeploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "parameters": {
      "policyName": {
          "type": "string",
          "metadata": {
              "description": "Provide name for the policyDefinition."
          }
      },
      "policyDescription": {
          "type": "string",
          "metadata": {
              "description": "Provide a description for the policy."
          }
      },
      "tagName": {
          "type": "string"
      }
    },
    "resources": [
        {
            "type": "Microsoft.Authorization/policyDefinitions",
            "apiVersion": "2019-09-01",
            "name": "[parameters('policyName')]",
            "properties": {
                "description": "[parameters('policyDescription')]",
                "displayName": "[parameters('policyName')]",
                "mode": "All",
                "policyRule": {
                  "if": {
                    "allOf": [
                      {
                        "field": "[concat('tags[', parameters('tagName'), ']')]",
                        "notEquals": "[subscription().tags[parameters('tagName')]]"
                      },
                      {
                        "value": "[subscription().tags[parameters('tagName')]]",
                        "notEquals": ""
                      }
                    ]
                  },
                  "then": {
                    "effect": "modify",
                    "details": {
                      "roleDefinitionIds": [
                        "/providers/microsoft.authorization/roleDefinitions/b24988ac-6180-42a0-ab88-20f7382dd24c"
                      ],
                      "operations": [
                        {
                          "operation": "addOrReplace",
                          "field": "[concat('tags[', parameters('tagName'), ']')]",
                          "value": "[subscription().tags[parameters('tagName')]]"
                        }
                      ]
                    }
                  }
                }
            }
        }
    ]
}