add-external-user-to-custom-lab.ps1

# Values to change
$subscriptionId = "<Enter Azure subscription ID here>"
$labResourceGroup = "<Enter lab's resource name here>"
$labName = "<Enter lab name here>"
$userDisplayName = "<Enter user's display name here>"

# Log into your Azure account
Login-AzAccount

# Select the Azure subscription that contains the lab. 
# This step is optional if you have only one subscription.
Select-AzSubscription -SubscriptionId $subscriptionId

# Retrieve the user object
$adObject = Get-AzADUser -SearchString $userDisplayName

# Create the role assignment. 
$labId = ('subscriptions/' + $subscriptionId + '/resourceGroups/' + $labResourceGroup + '/providers/Microsoft.DevTestLab/labs/' + $labName)
New-AzRoleAssignment -ObjectId $adObject.Id -RoleDefinitionName 'DevTest Labs User' -Scope $labId