Document Details

# NOTE: Before run this script ensure you are logged in Azure by using "az login" command.

$eventGridAppId = "[REPLACE_WITH_EVENT_GRID_APP_ID]"
$webhookAppObjectId = "[REPLACE_WITH_YOUR_ID]"
$eventSubscriptionWriterAppId = "[REPLACE_WITH_YOUR_ID]"


# Start execution
try {

    # Creates an application role of given name and description

    Function CreateAppRole([string] $Name, [string] $Description)
    {
        $appRole = New-Object Microsoft.Graph.PowerShell.Models.MicrosoftGraphAppRole
        $appRole.AllowedMemberTypes = New-Object System.Collections.Generic.List[string]
        $appRole.AllowedMemberTypes += "Application";
        $appRole.AllowedMemberTypes += "User";
        $appRole.DisplayName = $Name
        $appRole.Id = New-Guid
        $appRole.IsEnabled = $true
        $appRole.Description = $Description
        $appRole.Value = $Name;

        return $appRole
    }

    # Creates Azure Event Grid Microsoft Entra Application if not exists
    # You don't need to modify this id
    # But Azure Event Grid Entra Application Id is different for different clouds

    $eventGridSP = Get-MgServicePrincipal -Filter ("appId eq '" + $eventGridAppId + "'")
    if ($eventGridSP.DisplayName -match "Microsoft.EventGrid")
    {
        Write-Host "The Event Grid Microsoft Entra Application is already defined.`n"
    } else {
        Write-Host "Creating the Azure Event Grid Microsoft Entra Application"
        $eventGridSP = New-MgServicePrincipal -AppId $eventGridAppId
    }

    # Creates the Azure app role for the webhook Microsoft Entra application
    $eventGridRoleName = "AzureEventGridSecureWebhookSubscriber" # You don't need to modify this role name
    $app = Get-MgApplication -ApplicationId $webhookAppObjectId
    $appRoles = $app.AppRoles

    Write-Host "Microsoft Entra App roles before addition of the new role..."
    Write-Host $appRoles.DisplayName
    
    if ($appRoles.DisplayName -match $eventGridRoleName)
    {
        Write-Host "The Azure Event Grid role is already defined.`n"
    } else {      
        Write-Host "Creating the Azure Event Grid role in Microsoft Entra Application: " $webhookAppObjectId
        $newRole = CreateAppRole -Name $eventGridRoleName -Description "Azure Event Grid Role"
        $appRoles += $newRole
        Update-MgApplication -ApplicationId $webhookAppObjectId -AppRoles $appRoles
    }

    Write-Host "Microsoft Entra App roles after addition of the new role..."
    Write-Host $appRoles.DisplayName

    # Creates the user role assignment for the app that will create event subscription

    $servicePrincipal = Get-MgServicePrincipal -Filter ("appId eq '" + $app.AppId + "'")
    $eventSubscriptionWriterSP = Get-MgServicePrincipal -Filter ("appId eq '" + $eventSubscriptionWriterAppId + "'")

    if ($null -eq $eventSubscriptionWriterSP)
    {
        Write-Host "Create new Microsoft Entra Application"
        $eventSubscriptionWriterSP = New-MgServicePrincipal -AppId $eventSubscriptionWriterAppId
    }

    try
    {
        Write-Host "Creating the Microsoft Entra Application role assignment: " $eventSubscriptionWriterAppId
        $eventGridAppRole = $app.AppRoles | Where-Object -Property "DisplayName" -eq -Value $eventGridRoleName
        New-MgServicePrincipalAppRoleAssignment -ServicePrincipalId $eventSubscriptionWriterSP.Id -PrincipalId $eventSubscriptionWriterSP.Id -ResourceId $servicePrincipal.Id -AppRoleId $eventGridAppRole.Id 
    }
    catch
    {
        if( $_.Exception.Message -like '*Permission being assigned already exists on the object*')
        {
            Write-Host "The Microsoft Entra Application role is already defined.`n"
        }
        else
        {
            Write-Error $_.Exception.Message
        }
        Break
    }

    # Creates the service app role assignment for Event Grid Microsoft Entra Application

    $eventGridAppRole = $app.AppRoles | Where-Object -Property "DisplayName" -eq -Value $eventGridRoleName
    New-MgServicePrincipalAppRoleAssignment -ServicePrincipalId $eventGridSP.Id -PrincipalId $eventGridSP.Id -ResourceId $servicePrincipal.Id -AppRoleId $eventGridAppRole.Id 
    
    # Print output references for backup

    Write-Host ">> Webhook's Microsoft Entra Application Id: $($app.AppId)"
    Write-Host ">> Webhook's Microsoft Entra Application ObjectId Id: $($app.ObjectId)"
}
catch {
  Write-Host ">> Exception:"
  Write-Host $_
  Write-Host ">> StackTrace:"  
  Write-Host $_.ScriptStackTrace
}