template.json

{
    "$schema": "https://schema.management.azure.com/schemas/2015-01-01/deploymentTemplate.json#",
    "contentVersion": "1.0.0.0",
    "resources": [
        {
            "type": "Microsoft.Authorization/roleAssignments",
            "apiVersion": "2018-09-01-preview",
            "name": "[guid(resourceGroup().id)]",
            "properties": {
                "roleDefinitionId": "[concat('/subscriptions/', subscription().subscriptionId, '/providers/Microsoft.Authorization/roleDefinitions/', '8e3af657-a8ff-443c-a75c-2fe8c4bcb635')]",
                "principalId": "c3f78d62-59b9-4b5b-b70c-963d696efd7e"
            }
        }
    ]
}