Ensure that Activity Log Alert exists for Create Policy Assignment

Description:

Create an activity log alert for the Create Policy Assignment event.

Rationale:

Monitoring for create policy assignment events gives insight into changes done in "Azure policy - assignments" and can reduce the time it takes to detect unsolicited changes.

From Azure Portal

1. Navigate to the 'Monitor' blade.
2. Select 'Alerts'.
3. Select 'Create'.
4. Select 'Alert rule'.
5. Under 'Filter by subscription', choose a subscription.
6. Under 'Filter by resource type', select 'Policy assignment (policyAssignments)'.
7. Under 'Filter by location', select 'All'.
8. From the results, select the subscription.
9. Select 'Done'.
10. Select the 'Condition' tab.
11. Under 'Signal name', click 'Create policy assignment (Microsoft.Authorization/policyAssignments)'.
12. Select the 'Actions' tab.
13. To use an existing action group, click 'elect action groups'. To create a new action group, click 'Create action group'. Fill out the appropriate details for the selection.
14. Select the 'Details' tab.
15. Select a 'Resource group', provide an 'Alert rule name' and an optional 'Alert rule description'.
16. Click 'Review + create'.
17. Click 'Create'.

From Azure CLI

az monitor activity-log alert create --resource-group "" --condition category=Administrative and operationName=Microsoft.Authorization/policyAssignments/write and level=<verbose | information | warning | error | critical> --scope "/subscriptions/" --name "" --subscription --action-group --location global

From PowerShell

Create the 'conditions' object.

$conditions = @()
$conditions += New-AzActivityLogAlertAlertRuleAnyOfOrLeafConditionObject -Equal Administrative -Field category
$conditions += New-AzActivityLogAlertAlertRuleAnyOfOrLeafConditionObject -Equal Microsoft.Authorization/policyAssignments/write -Field operationName
$conditions += New-AzActivityLogAlertAlertRuleAnyOfOrLeafConditionObject -Equal Verbose -Field level

Get the 'Action Group' information and store it in a variable, then create a new 'Action' object.

$actionGroup = Get-AzActionGroup -ResourceGroupName -Name
$actionObject = New-AzActivityLogAlertActionGroupObject -Id $actionGroup.Id

Create the 'Scope' variable.

$scope = "/subscriptions/"

Create the 'Activity Log Alert Rule' for 'Microsoft.Authorization/policyAssignments/write'

New-AzActivityLogAlert -Name "" -ResourceGroupName "" -Condition $conditions -Scope $scope -Location global -Action $actionObject -Subscription -Enabled $true