For a customer use case in an Azure Marketplace Managed Application scenario, I needed the ability to translate the (customers’) Azure Subscription ID (which is known to the publishing tenant) to a tenant ID. Using Get-AzSubscription, Lighthouse subscriptions don’t show the true tenant ID of the other tenant, but only show your own tenant ID.

The following PS function can retrieve the tenant ID for you (without authentication):

function get-tenantIdFromSubscriptionID($subId){
    $response = try {(Invoke-WebRequest -UseBasicParsing -Uri "https://management.azure.com/subscriptions/$($subId)?api-version=2015-01-01" -ErrorAction Stop).BaseResponse} catch { $_.Exception.Response } 
    $stringHeader = $response.Headers.ToString()
    return($stringHeader.SubString($stringHeader.IndexOf("login.windows.net")+18,36))
}